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

resources/bin/README.md

@@ -6,15 +6,17 @@ asar archive) and are committed here so a fresh clone builds and runs.
 
 `ffmpeg.exe` + `ffprobe.exe` are **NOT shipped in the installer** — they're the bulk of
 its size, so they're downloaded on first run into `userData/bin` (see
-`src/main/ffmpegSetup.ts`, pinned in `src/main/config.ts`). The copies here are used only
-as a **dev seed** — `ensureManagedFfmpeg` copies them into `userData/bin` so `npm run dev`
-needs no download — and are excluded from the shipped build.
+`src/main/ffmpegSetup.ts`, pinned in `src/main/config.ts`). Dropping copies here is an
+**optional dev seed** — `ensureManagedFfmpeg` copies them into `userData/bin` so
+`npm run dev` needs no download — but at ~107MB each (over GitHub's 100MB file limit)
+they're **gitignored, not committed**. Without the seed, `npm run dev` just triggers the
+same first-run download the shipped app uses.
 
 ```
 resources/bin/
 ├── yt-dlp.exe     (bundled + committed)
-├── ffmpeg.exe     (dev seed only — excluded from the installer)
-├── ffprobe.exe    (dev seed only — excluded from the installer)
+├── ffmpeg.exe     (optional dev seed — gitignored, excluded from the installer)
+├── ffprobe.exe    (optional dev seed — gitignored, excluded from the installer)
 └── aria2c.exe     (optional, bundled)
 ```