Add fit-to-size two-pass encoding, file argument, recipes, and batch mode

- Fit to size: computes H.264 bitrate from duration and runs a
  two-pass encode to land on a target size in MB
- lazyff FILE opens straight in the editor
- Recipes: save/load named edit stacks (~/.config/lazyff/recipes.json)
- Batch: mark files with Space, run one edit stack across all of them
  through a sequential job queue with per-file results

README.md

@@ -19,11 +19,13 @@ learn FFmpeg as you use it (and copy-paste the command anywhere).
 cargo run --release
 # or
 cargo install --path .
-lazyff
+lazyff              # browse the current directory
+lazyff video.mp4    # open a file straight in the editor
 ```
 
 lazyff opens a file browser in the current directory. Pick a video or audio
-file, then stack up edits and press `r`.
+file, then stack up edits and press `r`. Mark several files with `Space` to
+edit them all at once (batch mode).
 
 ## What it can do
 
@@ -38,6 +40,7 @@ file, then stack up edits and press `r`.
 | Visual effects  | grayscale, sepia, blur, sharpen, vignette, denoise, fades |
 | Frame rate      | 12 – 60 fps                                           |
 | Compress        | H.264/H.265 with plain-English quality presets        |
+| Fit to size     | "make it 25 MB" — two-pass encode to a target size    |
 | Convert format  | MP4, MKV, WebM, MOV, GIF (with palette pass), MP3, M4A, WAV |
 | Audio           | remove track, volume, loudness normalization          |
 
@@ -53,7 +56,12 @@ them — trim, speed, volume/fades, and conversion between audio formats
 **File browser** — `↑↓` move, `Enter` open, `Backspace` parent folder, `q` quit
 
 **Editor** — `a` add edit, `Enter` change, `d` delete, `J`/`K` reorder,
-`o` output name, `r` run, `Esc` back to files, `q` quit
+`s` save recipe, `l` load recipe, `o` output name, `r` run, `Esc` back to
+files, `q` quit
+
+**Recipes** save your current stack of edits under a name
+(`~/.config/lazyff/recipes.json`) so you can re-apply it to any file or
+batch with two keys.
 
 **Forms** — `↑↓` field, `←→` change choice, type into text fields,
 `Enter` save, `Esc` cancel