Bug fix: Stats queries (eggs/day, feed/bird/day, etc.) were not excluding
tombstoned (deleted) events. Updated EventStore.list_events() to exclude
tombstoned events by default via LEFT JOIN, and updated direct SQL queries
in stats.py with the same tombstone exclusion.
New stats added:
- Harvest form: cost/egg (global, 30-day avg)
- Sell form: avg price/egg (30-day)
- Give feed form: cost/bird/day (global, 30-day avg)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Implements Step 2.2 of the plan:
- EventStore class with append_event, get_event, list_events, is_tombstoned
- Event type constants for all 17 event types from spec
- ClockSkewError for rejecting timestamps >5 min in future
- DuplicateNonceError for idempotency nonce validation
- 25 tests covering all event store functionality
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
