feat(8.0): temporal range verbs — diff, history, since(gen|Date), asOf{exclusive}, transactionLog window

asOf() answers "state AT a point"; these answer "what happened BETWEEN two
points" and "one entity's whole history", all on the existing generation records.

- Extract resolveAsOfGeneration() as the shared gen|Date→{generation,timestamp}
  chokepoint (reachability + Date semantics identical everywhere). asOf()'s
  inclusive path is byte-identical — db-mvcc still 25/25.
- asOf(target, { exclusive }) — strict-before (resolved−1, clamped at gen 0,
  never a RangeError).
- db.since(Db | generation | Date) — overload; number/Date resolve via the shared
  resolver (new DbHost.resolveGeneration); EXCLUSIVE lower bound;
  since(db) === since(db.generation). Same-store guard via Db.belongsToStore.
- brain.diff(a, b) → { added, removed, modified } split by nouns/verbs. EARNS its
  name: candidate set is ONLY changedBetween(gLow,gHigh), each classified by
  existence at both endpoints + a key-order-insensitive value compare
  (new src/db/stableEqual.ts) — a touched-but-reverted / born-and-died id is in
  no bucket.
- brain.history(id, { from, to }) → every distinct version oldest→newest, each
  value === asOf(version.generation).get(id); null = removal; kind auto-detected
  (throws on UUID-space collision). New store helper generationsTouching().
- brain.transactionLog({ from, to, limit }) — INCLUSIVE generation/Date window
  (contrast since's exclusive lower bound); limit applied last.
- Compaction policy locked: diff/since THROW GenerationCompactedError below the
  horizon; history TRUNCATES to it.

Types DiffResult/HistoryVersion/EntityHistory exported from the package root.
Tests: tests/integration/db-temporal.test.ts (8 proofs incl. diff-earns-its-name,
history↔asOf cross-check, the composition proof, granularity, compaction contrast)
+ tests/unit/db/stableEqual.test.ts (6). docs/guides/snapshots-and-time-travel.md
+ RELEASES updated. 1477 unit + db-temporal 8 + db-mvcc 25 green.

src/index.ts

@@ -172,7 +172,10 @@ export type {
   TxLogEntry,
   CompactHistoryOptions,
   CompactHistoryResult,
-  ChangedIds
+  ChangedIds,
+  DiffResult,
+  HistoryVersion,
+  EntityHistory
 } from './db/types.js'
 // Optional provider capability for generation-aware native indexes
 export { isVersionedIndexProvider } from './plugin.js'