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)

tests/integration/find-where-zero.test.ts

@@ -56,7 +56,7 @@ describe('BR-FIND-WHERE-ZERO regression', () => {
 
   describe('Reader sees correct entity counts after writer cold-start', () => {
     it('preserves entity count across writer→close→reader-open', async () => {
-      writer = new Brainy({ storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
       await writer.init()
       const writerIds = new Set<string>()
       for (let i = 0; i < 10; i++) {
@@ -80,7 +80,7 @@ describe('BR-FIND-WHERE-ZERO regression', () => {
     })
 
     it('preserves type classification (no "all entities are thing" poisoning)', async () => {
-      writer = new Brainy({ storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
       await writer.init()
       // Three types. Each id is tracked individually so we don't conflate
       // user-added entities with whatever VFS / auto-extraction inserts.
@@ -120,7 +120,7 @@ describe('BR-FIND-WHERE-ZERO regression', () => {
 
   describe('find() consistency', () => {
     it('returns entities that exist on disk (not silent empty)', async () => {
-      writer = new Brainy({ storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
       await writer.init()
       const conceptIds: string[] = []
       for (let i = 0; i < 4; i++) {
@@ -145,7 +145,7 @@ describe('BR-FIND-WHERE-ZERO regression', () => {
     })
 
     it('returns [] with a logged warning for unindexed field', async () => {
-      writer = new Brainy({ storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
       await writer.init()
       await writer.add({ data: 'test', type: NounType.Concept })
       await writer.flush()
@@ -162,7 +162,7 @@ describe('BR-FIND-WHERE-ZERO regression', () => {
     })
 
     it('raw getIds() throws BrainyError(FIELD_NOT_INDEXED) for unindexed field', async () => {
-      writer = new Brainy({ storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
       await writer.init()
       await writer.add({ data: 'test', type: NounType.Concept })
       await writer.flush()
@@ -181,7 +181,7 @@ describe('BR-FIND-WHERE-ZERO regression', () => {
 
   describe('explain() and health() match the new contract', () => {
     it('explain() returns column-store path for indexed fields', async () => {
-      writer = new Brainy({ storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
       await writer.init()
       await writer.add({
         data: 'test',
@@ -196,7 +196,7 @@ describe('BR-FIND-WHERE-ZERO regression', () => {
     })
 
     it('health() reports pass for a clean writer + reader handoff', async () => {
-      writer = new Brainy({ storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', rootDirectory: dir }, silent: true })
       await writer.init()
       for (let i = 0; i < 5; i++) {
         await writer.add({ data: `entry ${i}`, type: NounType.Concept })