Add a real VHS-recorded demo of writ to the README

[Laaaaksh]

Summary

• Records a genuine, unstaged end-to-end run of the writ CLI with VHS: propose → approve --yes → an in-scope edit that gets attested and leaves status clean/auto-mergeable → an out-of-scope edit that status flags as drift, while staying quiet about the in-scope work. That signal-vs-noise contrast is the whole pitch, and both runs are captured back to back.
• Adds docs/assets/demo.mp4 (1280px H.264/yuv420p, full quality) and docs/assets/demo.gif (960px, ~12fps palette-quantized, 832 KB — well under the 10 MB budget) for the README.
• Adds a ## Demo section to the README right after the intro/badges, embedding the GIF and linking the MP4 for full quality.
• Adds scripts/record-demo/record.sh + scripts/record-demo/demo.tape (the actual recording script, reviewable in the diff) + scripts/record-demo/README.md, and a Makefile with a demo target so the recording is one command (make demo) and reproducible.
• Documents the workflow in AGENTS.md so future agents regenerate the assets via make demo instead of hand-editing them.

Note: the task brief mentioned a possibly-unverified demo GIF already embedded in the README under docs/assets/. There wasn't one — README had no ## Demo section and docs/assets/ only held writ-banner.svg — so there was nothing to delete/replace beyond adding the new assets.

Test plan

• go build ./..., go vet ./..., gofmt -l . (clean), go test ./... all pass
• make demo runs end to end: builds the real binary, seeds a throwaway repo, records with VHS, converts with ffmpeg
• Verified docs/assets/demo.mp4 is H.264/yuv420p, 1280x800, 1148 frames (~46s)
• Verified docs/assets/demo.gif is 960x600, 551 frames, 832 KB
• Visually reviewed extracted frames: real terminal output, the clean auto-mergeable status (green) and the drift-flagged status (red, naming only the out-of-scope file) both genuinely appear
• Confirmed no old demo asset existed to delete (README/docs/assets had none)

🤖 Generated with Claude Code

https://claude.ai/code/session_01UjNjr48C8W9go9PmcNjdh6

[Laaaaksh]

Fixed the two cosmetic issues:

1. Empty dark space: Set Height dropped from 800 to 480 in demo.tape — the terminal now fits its content instead of leaving most of every frame empty.
2. Wrapping claim line: shortened the writ attest --note text so retries-on-5xx ... claimed by agent ... "retries Send on failure" fits on one line.

While verifying, I found the writ approved: <path> line was also wrapping for the same underlying reason (line too long for the terminal width) even though it wasn't called out — fixed it too by moving the throwaway demo repo from scripts/record-demo/.demo-repo to .demo-repo at the repo root, which shortens the absolute path writ prints.

Re-recorded end to end with make demo, re-verified: docs/assets/demo.mp4 is 1280x480 (1089 frames), docs/assets/demo.gif is 960x360 (523 frames, 868K — under the 10 MB budget), and I visually confirmed no line wraps anywhere in the loop.