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)

schemas/styles/playbook.schema.json

@@ -114,9 +114,21 @@
         "music_mood": { "type": "string" },
         "music_volume": { "type": "number", "minimum": 0, "maximum": 1 },
         "sfx_style": { "type": "string" },
-        "ducking_threshold_db": { "type": "number" }
-      },
-      "additionalProperties": false
+        "ducking_threshold_db": { "type": "number" },
+        "voice_variation_allowed": {
+          "type": "boolean",
+          "default": false,
+          "description": "Whether voice characteristics can shift between sections for emphasis"
+        },
+        "hero_moment_voice_shift": {
+          "type": "string",
+          "description": "How the voice should change for hero moments, e.g., 'slower, more deliberate, drop pitch'"
+        },
+        "transition_voice_shift": {
+          "type": "string",
+          "description": "How the voice should change at transitions, e.g., 'brief pause, then resume at slightly higher energy'"
+        }
+      }
     },
     "asset_generation": {
       "type": "object",
@@ -172,11 +184,36 @@
           "description": "Enable color-blind safety checking for palettes.",
           "type": "boolean"
         }
-      },
-      "additionalProperties": false
+      }
+    },
+    "overrides": {
+      "description": "Per-scene palette or rule exceptions. Up to 20% of scenes may intentionally deviate from the playbook for creative impact.",
+      "type": "object",
+      "properties": {
+        "max_deviation_ratio": {
+          "type": "number",
+          "minimum": 0,
+          "maximum": 0.5,
+          "default": 0.2,
+          "description": "Maximum fraction of scenes that may deviate from playbook defaults"
+        },
+        "scene_overrides": {
+          "type": "array",
+          "items": {
+            "type": "object",
+            "required": ["scene_id", "reason"],
+            "properties": {
+              "scene_id": { "type": "string" },
+              "reason": { "type": "string", "description": "Why this scene deviates from the playbook" },
+              "color_override": { "type": "object" },
+              "typography_override": { "type": "object" },
+              "motion_override": { "type": "object" }
+            }
+          }
+        }
+      }
     }
   },
-  "additionalProperties": false,
   "$defs": {
     "font_spec": {
       "type": "object",