feat: add historical state resolver with point-in-time queries

Implement resolve_filter() to resolve animals matching FilterAST at ts_utc.
Uses interval tables for historical location, sex, life_stage, and tags.
Includes roster hash computation using xxhash64.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PLAN.md

@@ -198,11 +198,11 @@ Check off items as completed. Each phase builds on the previous.
 - [x] **Commit checkpoint**
 
 ### Step 5.2: Historical State Resolver
-- [ ] Update `selection/resolver.py` for point-in-time resolution
-- [ ] Use interval tables for historical state (spec §7 query pattern)
-- [ ] Create `selection/hash.py` with roster hash (xxhash64)
-- [ ] Write tests: resolver returns correct animals before/after events
-- [ ] **Commit checkpoint**
+- [x] Update `selection/resolver.py` for point-in-time resolution
+- [x] Use interval tables for historical state (spec §7 query pattern)
+- [x] Create `selection/hash.py` with roster hash (xxhash64)
+- [x] Write tests: resolver returns correct animals before/after events
+- [x] **Commit checkpoint**
 
 ### Step 5.3: Optimistic Locking
 - [ ] Create `selection/validation.py` for selection validation