feat(ce-demo-reel): add demo reel skill with Python capture pipeline (#541)

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

plugins/compound-engineering/skills/ce-demo-reel/references/tier-screenshot-reel.md

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+# Tier: Screenshot Reel
+
+Render styled terminal frames from text and stitch into an animated GIF. Each frame shows one step of a CLI demo (command + output).
+
+**Best for:** CLI tools shown as discrete steps (command -> output -> next command -> output). Also useful when VHS breaks on quoting or special characters.
+**Output:** GIF (silicon PNGs stitched via ffmpeg)
+**Label:** "Demo"
+**Required tools:** silicon, ffmpeg
+
+## Step 1: Write Demo Content
+
+Create a text file with `---` delimiters between frames. Each frame shows the terminal state for one step:
+
+Write to `[RUN_DIR]/demo-steps.txt`:
+
+```
+$ your-cli-command --flag value
+Output line 1
+Output line 2
+Success: feature works correctly
+---
+$ your-cli-command --another-flag
+Different output showing another aspect
+Result: 42 items processed
+---
+$ your-cli-command --verify
+All checks passed
+```
+
+**Tips:**
+- Include the `$` prompt to show what the user types
+- Keep each frame under ~80 characters wide for readability
+- 3-5 frames is ideal -- enough to tell the story, not so many the GIF is huge
+- Strip unicode characters that silicon's default font can't render (checkmarks, fancy arrows)
+
+## Step 2: Split into Frame Files
+
+Split the demo content on `---` lines into separate text files, one per frame:
+
+- `[RUN_DIR]/frame-001.txt`
+- `[RUN_DIR]/frame-002.txt`
+- `[RUN_DIR]/frame-003.txt`
+- etc.
+
+## Step 3: Render and Stitch
+
+Use the capture pipeline script to render each text frame through silicon and stitch into an animated GIF in a single call:
+
+```bash
+python3 scripts/capture-demo.py screenshot-reel --output [RUN_DIR]/demo.gif --duration 2.5 --text [RUN_DIR]/frame-001.txt [RUN_DIR]/frame-002.txt [RUN_DIR]/frame-003.txt
+```
+
+The script handles silicon rendering, dimension normalization, two-pass palette generation, and automatic frame reduction if the GIF exceeds limits. Default duration is 2.5 seconds per frame (faster than browser reels since terminal frames are quicker to read).
+
+**If the script fails** (silicon rendering error, stitching error, empty output): fall back to static screenshots tier. Include the raw terminal output as a code block in the PR description instead. Label as "Terminal output", not "Screenshots".
+
+## Step 4: Cleanup
+
+Remove individual PNGs and text files. Keep only the final GIF for upload.
+
+Proceed to `references/upload-and-approval.md`.