remove per-write doltCommit from bun adapter

[timsehn]

Summary

The DoltliteClientAdapter in db.doltlite.bun.ts used to fire dolt_commit('-A','-m',…) after every autocommit write to a tracked table, and again after every wrapped transaction. This is the suspected cause of opencode's read-after-write failure on session creation (lines 305–308 of the captured SQL log on doltlite 0.10.0): INSERT INTO session returns changes=1, four immediately subsequent SELECT WHERE id=? return rows=0.

A secondary problem: the inTx flag was only set inside adapter.transaction(fn). Code that called db.exec("BEGIN TRANSACTION") directly — json-migration.ts does this — bypassed the gate, so each tracked-table insert inside that raw transaction called doltCommit while the SQL transaction was still open.

Both go away if the adapter stops trying to mirror SQL transactions into dolt history. dolt_commit is now strictly explicit; callers can snapshot at meaningful boundaries (shutdown, idle ticks, user action) instead of paying it on every write.

What's left in the adapter:

• client.transaction(fn).immediate() — drizzle-bun-sqlite needs bun:sqlite's transaction shape
• stmt.values() — drizzle-bun-sqlite reads rows-as-arrays through this

That's the entire surface drizzle-orm/bun-sqlite actually uses. 140 lines down to ~70.

Follow-up not in this PR

There is no automatic dolt snapshot anywhere now. A periodic + on-shutdown call to Database.Client().$client.doltCommit(…) (or equivalent hook in opencode's lifecycle) would restore that, with the right cadence.

Test plan

New packages/opencode/test/storage/db-adapter.test.ts pins the read-after-write contract through the same Drizzle entry points opencode uses:

• autocommit INSERT → SELECT sees the row
• BEGIN IMMEDIATE / INSERT / COMMIT → 4 retried SELECTs (the exact failing pattern from the log) all return rows=1
• BEGIN DEFERRED variant — same
• ROLLBACK throws and discards the insert
• 5 sequential BEGIN IMMEDIATE transactions are all visible afterwards

Existing coverage:

• 5/5 new adapter tests pass
• 40/41 storage tests pass (the one fail — db.test.ts:12, expects opencode-local.db vs current .ddb — is unrelated and pre-existed this branch)
• 43/43 SyncEvent + control-plane tests pass — these exercise the actual Database.transaction({behavior:"immediate"}) → projector → INSERT → COMMIT → SELECT path
• 2388/2402 full opencode suite passes

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