chore: stop tracking ffmpeg/ffprobe dev-seed binaries

They're >100MB each, redundant with the app's existing first-run download
(ffmpegSetup.ts), and blocked publishing the repo to GitHub (100MB file
limit). Gitignore them instead; npm run dev falls back to that download
when the seed is absent. Working-tree copies are kept locally for dev.

.gitignore

@@ -8,6 +8,11 @@ dist
 # Local screen-capture frames (not source)
 .frames/
 
+# Dev-seed only — too large for GitHub (>100MB); app downloads on first run
+# (src/main/ffmpegSetup.ts). See resources/bin/README.md to seed them manually.
+resources/bin/ffmpeg.exe
+resources/bin/ffprobe.exe
+
 # Secrets — never commit
 .gitea-token
 # Retired: the baked update token was removed from the build and its service