feat(ui): shared ListPane primitive + misc polish

ListPane is a compound component (Header / TitleRow / Title / Actions /
Search / Scroll) that owns the relative wrapper, faded right divider
(50px top fade), top scroll mask, and absolute-positioned header used by
every list-detail tab. Wires up CapturesTab, StoryList, and EffectsList.
EffectsTab gets -mx-8 / pr-8 to match the edge-to-edge layout used
elsewhere.

Other changes:
- MCPPage: native <select> → shadcn <Select> for default voice and
  per-binding voice pickers
- Button outline variant: add hover:border-accent
- Drop hover:text-destructive from trailing delete buttons
  (HistoryTable, GpuAcceleration, GpuPage, EffectsChainEditor,
  EffectsDetail)
- HistoryTable empty state moved behind t('history.empty')
- StoryContent scroll padding pt-14 → pt-16
- backend health reports the captures dir
- landing CapturesMockup: "Send to" → "Export" with Download icon
- CHANGELOG: drop [Unreleased] personality section

backend/routes/health.py

@@ -188,6 +188,7 @@ async def filesystem_health():
 
     dirs_to_check = {
         "generations": config.get_generations_dir(),
+        "captures": config.get_captures_dir(),
         "profiles": config.get_profiles_dir(),
         "data": config.get_data_dir(),
     }