feat(app): UI walkthrough pass — faithful screenshots, dock labels, timeline clips, status bar, meter

- screenshot example inits i18n and captures both zh-CN and en-US
  (docs/screenshot-window{,-en}.png)
- dock tabs size to content (no more 64px truncation); viewer/panel
  titles follow the design (素材查看器·name etc.)
- mock project carries V1/V2 video + A1/A2 audio clips rendered as
  rounded green bars; timeline clip geometry/rounded corners match the
  design; status bar visible with full content; audio meter strip
  docked at the program viewer's right edge; project explorer rows
  have icons
- tests/waveform_e2e.rs: waveform cache extracts real peaks and hits
  cache on re-query (P4 acceptance)

.gitignore

@@ -70,6 +70,7 @@ ui_*.h
 *.jsc
 Makefile*
 *build-*
+!tooling/ffmpeg/build-ffmpeg.sh
 *.qm
 *.prl