feat: add selection filter DSL parser

Implement parser for filter strings like "species:duck sex:female -tag:old".
Supports AND (space), OR (|), negation (-), and quoted values.

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

PLAN.md

@@ -190,12 +190,12 @@ Check off items as completed. Each phase builds on the previous.
 ## Phase 5: Selection & Historical Queries
 
 ### Step 5.1: Selection Filter DSL Parser
-- [ ] Create `selection/parser.py` for filter parsing
-- [ ] Support: AND (default), OR (|), negate (-), quotes
-- [ ] Fields: location, species, sex, life_stage, identified, tag
-- [ ] Create `selection/ast.py` for filter AST nodes
-- [ ] Write tests for all filter syntax variations
-- [ ] **Commit checkpoint**
+- [x] Create `selection/parser.py` for filter parsing
+- [x] Support: AND (default), OR (|), negate (-), quotes
+- [x] Fields: location, species, sex, life_stage, identified, tag
+- [x] Create `selection/ast.py` for filter AST nodes
+- [x] Write tests for all filter syntax variations
+- [x] **Commit checkpoint**
 
 ### Step 5.2: Historical State Resolver
 - [ ] Update `selection/resolver.py` for point-in-time resolution