Implementation spec: governance, decision intelligence, theme system, and E2E bug fixes

Implements the 2026-04-02 transformation spec (Phases 1-8) and fixes all
critical bugs found during 5-pipeline E2E testing.

Governance & Decision Intelligence:
- Pipeline-specific stage order in checkpoint (replaces global STAGES list)
- Provider scoring engine (lib/scoring.py) with 7-dimension weighted ranking
- Decision log artifact enforced at proposal/idea stage across all 10 pipelines
- Delivery promise classifier prevents silent motion-to-still downgrades
- Structured shot language in scene_plan schema (camera, lens, lighting, DOF)
- Variation checker and slideshow risk scorer block samey output before render
- Creative intake, capability extension, and creative-intake meta skills
- Final self-review artifact with 5 mandatory checks before presenting output
- Source media review contract for user-supplied footage

Render & Theme System:
- Remotion AnimatedBackground now derives colors from playbook (no more hardcoded
  dark blue fintech gradient on every video)
- video_compose builds custom ThemeConfig from playbook YAML colors/fonts —
  custom playbooks flow through to Remotion automatically
- Explainer component wires theme to all child components (charts, cards, etc.)
- resolveAsset() handles absolute paths on Windows/Unix via file:// URIs
- RENDERER_FAMILY_MAP synced with actual Remotion compositions

Critical Bug Fixes:
- Windows npx subprocess: run_command() resolves .cmd wrappers via shutil.which()
- Silent renderer downgrade: Remotion failure now returns explicit error with
  options instead of silently falling back to FFmpeg
- .env inline comment parsing strips trailing # comments from API keys
- concat_path UnboundLocalError in video_compose finally block
- audio_mixer and showcase_card capture=True kwarg bug
- Selector estimate_cost() calls fixed (_select_tool -> _select_best_tool)
- asset_manifest schema expanded with provider, license, subtype fields
- screen-demo subtitle_gen moved from required to optional tools
- Duration drift detection in post-render final review (>25% warns)

pipeline_defs/talking-head.yaml

@@ -8,6 +8,12 @@ category: talking_head
 stability: beta
 default_checkpoint_policy: guided
 
+extensions:
+  custom_scripts: true
+  custom_playbooks: true
+  custom_skills: true
+  custom_tools: false
+
 required_skills:
   - pipelines/talking-head/executive-producer
   - pipelines/talking-head/idea-director
@@ -35,6 +41,7 @@ stages:
     skill: pipelines/talking-head/idea-director
     produces:
       - brief
+      - decision_log
     tools_available: []
     checkpoint_required: true
     human_approval_default: true
@@ -50,6 +57,8 @@ stages:
     skill: pipelines/talking-head/script-director
     required_artifacts_in:
       - brief
+    optional_artifacts_in:
+      - source_media_review
     produces:
       - script
     required_tools:
@@ -156,6 +165,7 @@ stages:
       - scene_plan
     produces:
       - render_report
+      - final_review
     required_tools:
       - video_compose    # rendering
       - audio_mixer      # audio layering + segmented music
@@ -201,6 +211,7 @@ stages:
     skill: pipelines/talking-head/publish-director
     required_artifacts_in:
       - render_report
+      - final_review
     produces:
       - publish_log
     tools_available: []