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/distributed-demo.test.ts

@@ -19,7 +19,7 @@ describe('Distributed Brainy Demo', () => {
   
   beforeAll(async () => {
     // Node 1: First node starts cluster
-    node1 = new Brainy({
+    node1 = new Brainy({ requireSubtype: false,
       storage: {
         s3Storage: {
           bucket: process.env.S3_BUCKET || 'brainy-test',
@@ -34,7 +34,7 @@ describe('Distributed Brainy Demo', () => {
     console.log('Node 1 started - became cluster leader')
     
     // Node 2: Automatically discovers and joins
-    node2 = new Brainy({
+    node2 = new Brainy({ requireSubtype: false,
       storage: {
         s3Storage: {
           bucket: process.env.S3_BUCKET || 'brainy-test',
@@ -49,7 +49,7 @@ describe('Distributed Brainy Demo', () => {
     console.log('Node 2 started - automatically joined cluster')
     
     // Node 3: Also joins automatically
-    node3 = new Brainy({
+    node3 = new Brainy({ requireSubtype: false,
       storage: {
         s3Storage: {
           bucket: process.env.S3_BUCKET || 'brainy-test',
@@ -114,7 +114,7 @@ describe('Distributed Brainy Demo', () => {
   
   it('should automatically rebalance when nodes join', async () => {
     // Start a new node
-    const node4 = new Brainy({
+    const node4 = new Brainy({ requireSubtype: false,
       storage: {
         s3Storage: {
           bucket: process.env.S3_BUCKET || 'brainy-test',
@@ -170,7 +170,7 @@ describe('Distributed Brainy Demo', () => {
 export function distributedExample() {
   return `
 // Zero-Config Distributed Setup
-const brain = new Brainy({
+const brain = new Brainy({ requireSubtype: false,
   storage: {
     s3Storage: {
       bucket: 'my-data',