Mobile Markdown extension proof

Surface: Android API 36, Pixel 9 emulator, 1080x2424, light theme.
Base: c2b06f9df8491cde7f707e62506aaff1183b19a3
Head: 49203886e81ae9c3cd7a8d8006def58c33c1970f

Each commit ran from its own worktree with its own fresh T3 home and Metro.
T3CODE_DEV_SEED=0 prevented copying existing user data. The server's scenario
start-app helper supplied the replay provider and a synthetic environment label.
The cached Android development client had the same native fingerprint on both
commits; mobile:install installed it for each side, then Metro supplied that
commit's JavaScript. Pair each side with its own server and open its seeded thread.

Place seed.ts in scripts/ beside scenarios/ in the tested checkout, then run:
T3_SCENARIO_APP_DIR=<checkout> node scripts/seed.ts <fresh-t3-home> <server-port>
It uses the repository's scenario helpers to create a synthetic project and replay
thread. All six files contain the same heading and two Markdown list items.

Starting on the thread screen, run:
python3 drive.py before <output-directory> <agent-device-session>
python3 drive.py after <output-directory> <agent-device-session>
Use the first command on base and the second on head. The driver opens each file,
opens File actions, captures the menu, selects Preview when present, and captures
the result. Its stills require two identical screenshots at least 500 ms apart.
It records the entire interaction; Android splits recordings at 180 seconds.

Overview PNGs crop only empty lower screen space and the status bar, and arrange
all six original captures in order: README.md, CHANGELOG.markdown, notes.MDOWN,
todo.mkd, draft#1.markdown, draft?1.mdown. Full original captures are also supplied.

For a recording without duplicate still-capture pauses, set PROOF_VIDEO_ONLY=1.
The driver waits for each file list, file menu, and rendered heading.

PROOF_FILES accepts a JSON array to record a subset of files. The final before
video joins Android recording chunks. The final after video joins the control
and .markdown clip with four single-file clips because larger exports failed.
The first after clip ends before a failed attempt to open the next file; no
menu or preview interaction was removed.