screen-demo: add synthetic-terminal mode via Remotion TerminalScene

Make synthetic screen recording a first-class, discoverable capability
alongside real OS capture. For CLI / terminal / install-flow demos where
commands and output are predictable, author a `terminal_scene` cut instead
of driving a real screen recorder — deterministic, privacy-safe, pixel-
perfect, and frame-accurate to narration cues.

Components:
- TerminalScene.tsx: window chrome, char-by-char typing, blinking cursor,
  scrolling output, non-blocking floating pills, spring-based reveals
- ProviderChip.tsx: rotating badge overlay that cycles through provider
  names (used in AI-generated-motion scenes)
- BackgroundVideoLayer + source_in_seconds + backgroundVideo props on
  every scene type — supports video-behind-component composition

Discovery chain (six layers, so the next agent finds this without reading
source code):

1. pipeline_defs/screen-demo.yaml — bump to 2.1, declare production_modes
   (real_capture, synthetic_terminal) with required_tools, scene_type, and
   agent_skills pointers
2. skills/pipelines/screen-demo/idea-director.md — mode-selection table
   at brief time; brief.metadata.production_mode contract
3. skills/pipelines/screen-demo/asset-director.md — reads production_mode
   and branches asset production (capture+overlays vs steps+narration+
   pacing check)
4. .agents/skills/synthetic-screen-recording/SKILL.md — Layer 3 skill with
   step kinds (cmd/out/pause/pill), pacing rule, and the frozen-terminal
   failure mode captured from the showcase v3 retune
5. AGENT_GUIDE.md — TerminalScene added to Remotion routing; links
   SCENE_TYPES.md as the authoritative cut-type registry
6. remotion-composer/SCENE_TYPES.md — new cheat sheet of every cut.type
   and overlay.type with required fields, plus a "how to add a new scene
   type" section (candidates: ChatTranscript, EditorScene, PrReview,
   SlackThread, TicketBoard)

Guardrail:
- lib/verify_scene_pacing.py — reusable trace() and assert_alignment()
  helpers that mimic the TerminalScene frame math exactly. Fail loudly
  before render if steps burn through too fast or leave the scene frozen.

pipeline_defs/screen-demo.yaml

@@ -1,14 +1,45 @@
 name: screen-demo
-version: "2.0"
+version: "2.1"
 description: >
-  Screen recording pipeline. Takes raw screen capture (app demo, browser walkthrough,
-  coding tutorial) and produces a polished demo video with callouts, zoom crops,
-  subtitles, and cleaned audio. EP orchestration adds quality gates for legibility,
-  audio clarity, and pacing.
+  Screen recording pipeline. Two production modes:
+    1. REAL CAPTURE — takes raw screen capture (app demo, browser walkthrough,
+       coding tutorial) via screen_recorder, cap_recorder, or playwright-recording
+       and produces a polished demo video with callouts, zoom crops, subtitles,
+       and cleaned audio.
+    2. SYNTHETIC (Remotion TerminalScene) — for CLI/terminal/install-flow demos,
+       renders a deterministic terminal animation with typed commands, scrolling
+       output, floating command pills, and blinking cursor. See
+       .agents/skills/synthetic-screen-recording/SKILL.md. Preferred when the
+       demo content is predictable (install walkthroughs, make targets, git clone,
+       API key config) because it's faster to iterate, privacy-safe, pixel-perfect,
+       and frame-accurate to narration cues.
+  The idea-director picks the mode at brief time based on whether the demo surface
+  is a real app UI (real capture) or a scriptable terminal session (synthetic).
 category: screen_recording
 stability: production
 default_checkpoint_policy: guided
 
+# Production modes this pipeline supports
+production_modes:
+  - name: real_capture
+    description: "OS screen recording of a real desktop/browser session"
+    required_tools: [screen_recorder]
+    optional_tools: [cap_recorder]
+    best_for:
+      - Real app UIs (Figma, Photoshop, web apps with live state)
+      - Demos that depend on unpredictable live behavior
+      - User explicitly asked for a recording of their own screen
+  - name: synthetic_terminal
+    description: "Remotion TerminalScene — synthesized terminal animation"
+    required_tools: [video_compose]  # Remotion path
+    scene_type: terminal_scene
+    agent_skills: [synthetic-screen-recording]
+    best_for:
+      - CLI / terminal / coding session demos
+      - Install walkthroughs, setup demos, config flows
+      - Tight narration-synced pacing where every command lands on a beat
+      - Reproducible renders (same input = identical pixels)
+
 orchestration:
   mode: executive-producer
   skill: pipelines/screen-demo/executive-producer