feat: verb subtype + updateRelation + requireSubtype enforcement

Brings verbs to first-class parity with nouns. The 7.29.0 subtype primitive
shipped for entities only; this release ships the symmetric verb mirror plus
the enforcement layer for ensuring every entity AND every relationship has
both type AND subtype.

Layer V1 — verb subtype mirror
- HNSWVerbWithMetadata.subtype + STANDARD_VERB_FIELDS set + resolveVerbField()
- Relation<T>.subtype, RelateParams<T>.subtype, UpdateRelationParams<T> extended,
  GetRelationsParams.subtype, GraphConstraints.subtype (for find connected)
- relate() persists subtype on verbMetadata + GraphVerb + transaction ops
- getRelations({ type, subtype }) fast-path filter with set membership
- find({ connected: { via, subtype, depth } }) traversal filter (depth-1 on
  the JS path; explicit error on depth > 1 pointing at Cortex native)
- verbsToRelations + storage destructure sites surface subtype to top-level
- All three graph-index fast-path queries (getVerbsBySource/ByTarget) enrich
  with subtype from metadata

Layer V2 — updateRelation() closes a pre-7.30 gap
- New first-class verb update method (parallel to update() for nouns)
- Changes subtype/type/weight/confidence/data/metadata in place
- Re-indexes in graph adjacency when verb type changes; id preserved
- validateUpdateRelationParams enforces id + at-least-one-field-to-update

Layer V3 — verb subtype storage rollup
- verbSubtypeCountsByType: Map<number, Map<string, number>> on BaseStorage
- verbSubtypeByIdCache for self-heal during update/delete
- incrementVerbSubtypeCount + decrementVerbSubtypeCount maintain state
- loadVerbSubtypeStatistics + saveVerbSubtypeStatistics persist to
  _system/verb-subtype-statistics.json (mirrors noun-side shape)
- rebuildVerbSubtypeCounts for poison recovery / explicit repair
- getVerbSubtypeCountsByType accessor for the public counts API
- Wired into init() / flushCounts() / saveVerbMetadata / deleteVerbMetadata

Layer V4 — verb counts API + relationshipSubtypesOf
- brain.counts.byRelationshipSubtype(verb, subtype?) — O(1) breakdown or point
- brain.counts.topRelationshipSubtypes(verb, n) — top N by count
- brain.relationshipSubtypesOf(verb) — sorted distinct subtypes

Layer V5 — migrateField extended to verbs
- New entityKind?: 'noun' | 'verb' | 'both' option (default 'noun')
- Mirror verb iteration via storage.getVerbs() with same path semantics
- verbToRelationLike + buildRelationMigrationUpdate helpers project the
  storage verb shape onto the Entity<T>-shaped surface readPath understands
- Routes through new updateRelation() for the verb-side rewrite

Enforcement (opt-in in 7.30, default in 8.0)
- brain.requireSubtype(type, options) — unified API for NounType OR VerbType.
  Registers per-type rules with optional values whitelist; composes with the
  brain-wide flag.
- new Brainy({ requireSubtype: true }) — brain-wide strict mode. Every public
  write path validates the pairing guarantee.
- { except: [NounType.Thing, ...] } form for catch-all type exemptions
- Atomic-fail semantics on addMany / relateMany — pre-validate every item
  before any storage write, throw on first failure with item index
- Per-type rules + brain-wide flag both throw with descriptive messages
- VFS infrastructure bypass via metadata.isVFSEntity / isVFS markers so
  brain's own VFS writes don't get rejected when strict mode is on

VFS labeling — concrete subtypes for infrastructure entities
- VFS root: NounType.Collection + subtype: 'vfs-root' (was bare Collection)
- VFS directories: subtype: 'vfs-directory'
- VFS files: subtype: 'vfs-file' (NounType still mime-based)
- VFS containment edges: VerbType.Contains + subtype: 'vfs-contains'
- Lets consumers cleanly enumerate VFS state via find({ subtype: 'vfs-file' })
  and distinguish Brainy's VFS Collections from user-created Collections

Docs
- docs/guides/subtypes-and-facets.md extended with Layer V (Verbs) section +
  Enforcement section. New full reference at the bottom split into Layer 1
  (nouns), Layer V (verbs), Layer 2 (facets), Layer 3 (migration), Enforcement.
- docs/api/README.md adds updateRelation(), getRelations({ subtype }), the
  three verb-side counts methods, requireSubtype(), and the brain-wide
  constructor option. relate() params include subtype.
- docs/DATA_MODEL.md adds a Subtype-for-VerbType section + STANDARD_VERB_FIELDS
- docs/architecture/finite-type-system.md extends Principle 1a to verbs
- docs/QUERY_OPERATORS.md adds a verb-subtype filter section covering
  getRelations and find({connected, subtype}) traversal
- README.md "Subtypes" section now shows both noun + verb in one example +
  the enforcement APIs
- RELEASES.md v7.30.0 entry with the full noun/verb capability parity matrix

Tests
- tests/integration/verb-subtype-and-enforcement.test.ts — 30 new tests
  covering V1 round-trips, V1 set membership, updateRelation in place,
  updateRelation preservation, V2 counts breakdown + point + topN + distinct,
  V2 decrements on unrelate, V2 re-routes on updateRelation, V3 depth-1
  traversal filter, V3 depth>1 explicit error, V4 verb migration, V4 both
  entity kinds, V4 readBoth preservation, V5 per-type required rejection,
  V5 vocabulary rejection, V5 on-vocab acceptance, V5 verb-side enforcement,
  V5 addMany atomic-fail, V5 relateMany atomic-fail, V5 update enforcement,
  V5 updateRelation enforcement, V5 brain-wide strict mode, V5 except clause.

Verification
- Unit suite: 1468/1468 passing
- Noun subtype integration (7.29 carryover): 26/26 passing
- Verb subtype + enforcement integration: 30/30 passing
- Type-check: clean
- Build: clean
- Public closed-source reference audit: clean

Internal 8.0 spec
- .strategy/BRAINY-8.0-SUBTYPE-CONTRACT.md (gitignored, not in npm artifact)
  documents the contract upgrade Cortex 3.0 implements against: required-by-
  default subtype, SubtypeRegistry typing hook, native simplification,
  multi-hop traversal native fast path, brain.fillSubtypes() migration helper.
  Coordinated via PLATFORM-HANDOFF rows CTX-SUBTYPE-PARITY-V2 (7.30 parallel
  work) and CTX-SUBTYPE-8.0-CONTRACT (8.0 spec).

docs/DATA_MODEL.md

@@ -221,6 +221,47 @@ await brain.add({
 
 `subtype` lives at the **top level** — NOT inside `metadata`, NOT inside `data`. That's how `find({ type, subtype })` routes through the standard-field fast path (column-store hit) instead of the metadata fallback. See **[Subtypes & Facets](./guides/subtypes-and-facets.md)** for the full guide including `trackField()` and `migrateField()`.
 
+### Subtype — sub-classification within a VerbType (7.30+)
+
+Relationships are first-class citizens too. Every verb (`VerbType`) gets the same `subtype` primitive — a `ReportsTo` relationship might carry `subtype: 'direct'` vs `'dotted-line'`; a `RelatedTo` edge might carry `'spouse'` / `'sibling'` / `'colleague'`. Same shape as the noun side: flat string, no hierarchy, top-level standard field on `HNSWVerbWithMetadata` and on the public `Relation<T>`:
+
+```typescript
+await brain.relate({
+  from: ceoId,
+  to: vpId,
+  type: VerbType.ReportsTo,
+  subtype: 'direct',                  // top-level standard field
+  metadata: { since: '2025-Q1' }      // user-custom fields stay in metadata
+})
+```
+
+Fast-path filter on the verb side:
+
+```typescript
+const direct = await brain.getRelations({
+  from: ceoId,
+  type: VerbType.ReportsTo,
+  subtype: 'direct'
+})
+```
+
+The verb-side rollup at `_system/verb-subtype-statistics.json` mirrors the noun-side `_system/subtype-statistics.json` — same shape, same self-heal machinery. Per-VerbType-per-subtype counts are O(1) via `brain.counts.byRelationshipSubtype()`.
+
+Verbs and nouns now have full capability parity — every API on the noun side has a verb-side mirror, including the new `brain.updateRelation()` (which closed a pre-7.30 gap where relationships had no update path).
+
+### Standard verb fields
+
+The verb-side equivalent of `STANDARD_ENTITY_FIELDS` is `STANDARD_VERB_FIELDS`, exported from `src/coreTypes.ts`. Verb-specific standard fields:
+
+| Field | Description |
+|---|---|
+| `verb` | The VerbType enum value |
+| `sourceId` / `targetId` | The two endpoints of the relationship |
+| `subtype` | Sub-classification within the VerbType (7.30+) |
+| `confidence`, `weight`, `createdAt`, `updatedAt`, `service`, `createdBy`, `data` | Same semantics as the noun-side standard fields |
+
+The companion `resolveVerbField(verb, field)` helper resolves field paths the same way `resolveEntityField` does for nouns: standard fields first, metadata fallback for everything else.
+
 ---
 
 ## See Also