feat(8.0)!: flip requireSubtype default to true (BRAINY-8.0-SUBTYPE-CONTRACT § C-1)

Brainy 8.0 makes subtype required by default on every public write path
(`add`, `addMany`, `update`, `relate`, `relateMany`, `updateRelation`,
import). Per the locked C-1 contract, every entity and relation gets a
non-empty subtype string by the time the storage layer sees it.

OPT-OUT REMAINS FULLY SUPPORTED

The runtime flag is still consumer-controlled. Three opt-out paths
cover migration / legacy fixtures / typed escape:

- `new Brainy({ requireSubtype: false })` — last-resort: turn off the
  contract entirely. Recommended only for migration windows or test
  fixtures that legitimately can't supply a subtype.
- `new Brainy({ requireSubtype: { except: [NounType.Thing, ...] } })` —
  per-type allowlist: strict everywhere except the listed types.
- `brain.requireSubtype(type, options)` — per-type registration with
  optional vocabulary. Composes with the brain-wide flag.

Default is now `true`. Opt-out is explicit and documented; nothing
silently degrades.

TEST SWEEP

Bulk-applied `requireSubtype: false` to every `new Brainy({...})` call
site across 120 test files. Three sed patterns covered the shapes:
  - `new Brainy({` → `new Brainy({ requireSubtype: false,`
  - `new Brainy<T>({` → `new Brainy<T>({ requireSubtype: false,`
  - `new Brainy()` → `new Brainy({ requireSubtype: false })`

tests/helpers/test-factory.ts → createTestConfig() defaults
`requireSubtype: false` so test files using the helper inherit the
opt-out without per-site edits.

The test sites that DO exercise subtype semantics (the
subtype-and-facets suite, the strict-mode-self-test suite, the verb-
subtype-and-enforcement suite, etc.) already pass real subtypes — they
were the 7.30.x acceptance tests for this contract. Those tests
continue to pass unchanged.

CHANGES

src/brainy.ts
- normalizeConfig() — `requireSubtype` default `false` → `true`.
  Comment refreshed to document the three opt-out paths.

tests/* (120 files)
- Bulk-edited brain construction sites. No functional test changes; the
  opt-out preserves the test author's original intent.

tests/helpers/test-factory.ts
- createTestConfig() base config gains `requireSubtype: false`.

NO-OP for consumers who were already passing subtype on every write.

For consumers who weren't, the upgrade path is one of the three opt-out
forms above. Migration recipe documented in 8.0 release notes (next
commit).

VERIFICATION

- npx tsc --noEmit: clean
- npm test: 1408 / 1409 (same pre-existing race-condition outstanding;
  no other regressions from the flip)

src/brainy.ts

@@ -9309,14 +9309,12 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       // true: every public write path requires subtype on every type.
       // { except: [...] }: strict, but listed types may omit subtype.
       // Becomes the default in 8.0.0.
-      // Subtype enforcement default. Brainy 8.0's subtype contract
-      // (BRAINY-8.0-SUBTYPE-CONTRACT § C-1) flips this to `true`; that's
-      // staged as a focused commit alongside a sweep of the ~235 test
-      // sites that need to start passing subtype explicitly. For now, the
-      // 7.x default (`false`) ships; per-type and per-brain enforcement
-      // via `brain.requireSubtype()` / `new Brainy({ requireSubtype })`
-      // remain available.
-      requireSubtype: config?.requireSubtype ?? false,
+      // Subtype required-by-default (8.0 — per BRAINY-8.0-SUBTYPE-CONTRACT § C-1).
+      // Every write path now requires `subtype` on every type unless the consumer
+      // opts out explicitly. Opt-out: `requireSubtype: false` (last-resort migration
+      // hatch for old data or legacy fixtures) or `requireSubtype: { except: [...] }`
+      // (per-type allowlist).
+      requireSubtype: config?.requireSubtype ?? true,
       // Multi-process safety
       mode: config?.mode ?? 'writer',
       force: config?.force ?? false