perf(cli): ingesting one call rewrites its whole month #1001

Problem

Ingesting one call rewrites its whole month partition of the usage ledger (usage-ledger-adapter.ts). At 265k records that takes about 3 s, measured for #993. It runs in the async catch-up hook, so no session waits, but the cost grows with the month.

Scope

• Make an ingest cost what it adds, not the size of its month.
• Keep what the rewrite guarantees today: one record per call (message.id:requestId, per tool), the largest total wins, written under the lock and only when content changes.

Acceptance criteria

• One call ingested into a 265k-record month in under 1 s, measured as in feat(telemetry): deterministic claude code token measurement, release 1 #993.
• The fold rules and the real-history oracle (262,328 calls, 68 days, no day differing) still hold.