feat(session-persistence-sqlite): second backend validating the abstraction

Add a SQLite SessionPersistence backend (node:sqlite), a SECOND
implementation built to prove the abstract seam + the shared
runPersistenceContract suite are genuinely backend-agnostic. Each
SessionEvent maps 1:1 onto an events row (session_id, seq, type, time,
data); append is an INSERT inside a transaction asserting the
contiguous-seq contract; the mutable SessionSummary lives in the
sessions metadata row.

It satisfies the SAME contract semantics as the JSONL backend, expressed
over rows instead of file bytes:
- Lazy materialization: create() records intent in memory; no row until
  the first append (a never-appended session is absent from has()/list()
  via a materialized flag set inside the first append transaction).
- Crash-tail-on-load: load() returns events only through the last
  complete turn/end and deletes the uncommitted tail; a seq gap in the
  committed region makes the session unloadable.
- Transactional append: a mid-batch failure (a UNIQUE seq collision from
  a concurrent writer) rolls back entirely, keeping the cursor truthful.

Like the JSONL backend it is also the write-path plugin (session/event →
buffer → session/flush drain, onCreated seed/adopt/collision handling,
HMR seeding, dispose-to-quiescence). The package runs the shared
runPersistenceContract suite plus SQLite-specific tests (transaction
rollback, crash-tail cut, schema version, HMR adoption).

Docs flip every "SQLite is future/deferred" reference (ADR 0016,
architecture.md, the persistence module doc + README) to "implemented;
the contract holds both backends to identical semantics".

scripts/publint-all.ts

@@ -8,6 +8,7 @@ const packages = [
   'packages/session',
   'packages/session-persistence',
   'packages/session-persistence-jsonl',
+  'packages/session-persistence-sqlite',
   'packages/system-prompt',
   'packages/tools',
   'packages/agent',