docs: fix schema link and expand storage/ledger reference

[cursor]

Docs added/updated

docs/release-artifact.md

• Fixed broken JSON Schema link: schemas/v1/release_artifact.schema.json → schemas/v1/release.schema.json (the file that actually exists in the repo; caught by comparing the doc link against ls schemas/v1/).

docs/operations-and-policy.md

• SQLite table list corrected: Added the missing pricing_import_audit table (7 tables, not 5/6).
• Storage connection settings: Documents the four SQLite pragmas (WAL, IMMEDIATE, busy_timeout=5000, foreign_keys=ON) and why BEGIN IMMEDIATE is used for promotion and pricing-import transactions.
• Idempotent run event ingestion: Explains the per-row insert loop, run_id PRIMARY KEY deduplication, safe re-ingest semantics, and what the return value represents.
• Schema migration table: Documents versions 1–3 (initial schema, run_events index, audit_seq column/backfill) and guidance for future migrations.
• Rollup semantics section: Covers how runs, cost_per_run_usd, latency_ms_avg, and error_rate are computed; clarifies run_start vs run_end event counting; explains latency_ms_avg = None (not zero) and the policy skip; documents the delta_cost_per_run_pct and delta_latency_ms_avg None guards.
• Active policy upsert behavior: Documents the INSERT … ON CONFLICT DO UPDATE single-row semantics and get_active_policy tie-breaking by updated_at.

Which codepaths these cover

Doc change	Source file
Schema link fix	schemas/v1/release.schema.json
Storage pragmas / transactions	src/flightdeck/storage.py (_configure_connection, transaction)
Idempotent ingest	src/flightdeck/storage.py (insert_run_events)
Schema migration table	src/flightdeck/storage.py (migrate, LATEST_SCHEMA_MIGRATION_VERSION)
Rollup semantics	src/flightdeck/ledger.py (compute_rollup, diff_releases, DiffResult)
Active policy upsert	src/flightdeck/storage.py (set_active_policy, get_active_policy)

Key knowledge gaps addressed

1. Broken link — the release artifact JSON Schema link pointed to a non-existent file name.
2. Missing table — pricing_import_audit was documented in the release-artifact doc but absent from the storage schema table in operations-and-policy.
3. Transaction model — BEGIN IMMEDIATE and WAL pragmas were undocumented; relevant to anyone debugging SQLITE_BUSY errors or concurrent access.
4. Idempotent ingest — the safe re-ingest guarantee was only visible in source code; operators need to know re-running runs ingest is harmless.
5. Rollup event counting — whether run_start events are counted was not documented; latency/delta None vs 0 distinction was missing.
6. Active policy ambiguity — behavior when multiple policy_id values exist was undocumented.