Phase 1 implementation: script ingestion + AI extraction pipeline

Complete working pipeline from Fountain script to validated scene JSON:
- Schemas (Pydantic): all 7 layers defined upfront
- Fountain parser + normalizer (Layer 1)
- AI scene extractor with prompt contracts (Layer 2)
- Schema validator + scene-specific semantic validator
- Structured JSON logging per layer/scene execution
- Versioned output writer (never overwrites)
- Retry engine with 4-level failure escalation
- Stop condition evaluator (per-unit + global halts)
- Diff/drift detector for re-run comparison
- CLI entry point with --dry-run, --scene, --test, --force
- 3 test scripts (dialogue-heavy, action-heavy, nonstandard)
- Expected output files for regression testing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test_scripts/expected/action_heavy_scenes.json

@@ -0,0 +1,7 @@
+{
+  "expected_scene_count": 18,
+  "expected_characters": ["JACK", "SOFIA", "RAMOS", "VEGA"],
+  "expected_locations": ["ROOFTOP", "ALLEY", "COMPOUND", "DRAINAGE TUNNEL", "STAIRWELL", "SUV", "HIGHWAY", "AIRSTRIP", "PROP PLANE"],
+  "must_not_contain_characters": [],
+  "must_not_contain_locations": []
+}

test_scripts/expected/dialogue_heavy_scenes.json

@@ -0,0 +1,7 @@
+{
+  "expected_scene_count": 13,
+  "expected_characters": ["MARCUS", "DR. VOSS", "LILY", "HENRY", "NURSE PATRICIA"],
+  "expected_locations": ["THERAPIST'S OFFICE", "APARTMENT", "COFFEE SHOP", "HOSPITAL ROOM", "HOSPITAL CAFETERIA", "HOSPITAL HALLWAY"],
+  "must_not_contain_characters": [],
+  "must_not_contain_locations": []
+}

test_scripts/expected/nonstandard_scenes.json

@@ -0,0 +1,7 @@
+{
+  "expected_scene_count": 11,
+  "expected_characters": ["NADIA", "DEREK", "TOMMY", "MRS. PETROV", "MOTHER"],
+  "expected_locations": ["APARTMENT", "GROCERY STORE", "PARKING LOT", "BUS STOP", "BUS", "GAS STATION", "FAMILY HOUSE", "MOTEL ROOM"],
+  "must_not_contain_characters": [],
+  "must_not_contain_locations": []
+}