feat(ui): theme settings, stories polish, track editor restructure

- add dark/light/system theme with persisted choice + OS change listener
- restyle stories sidebar (search, item layout, border) to match captures
- move floating generate box to right column of stories, add top fade mask
- story track editor: sticky track labels aligned via flex rows, custom scrollbar with left/right zoom handles
- capture pill light mode pass, fix inline waveform progress color
- pull mcp_server hidden imports into the pyinstaller spec
- notarization doc draft

app/src/components/Generation/FloatingGenerateBox.tsx

@@ -255,10 +255,10 @@ export function FloatingGenerateBox({
     <motion.div
       ref={containerRef}
       className={cn(
-        'fixed right-auto',
+        'fixed',
         isStoriesRoute
-          ? // Position aligned with story list: after sidebar + padding, width 360px
-            'left-[calc(5rem+2rem)] w-[360px]'
+          ? // Aligned with StoryContent: sidebar + list width + gap (tab bleeds with -mx-8)
+            'left-[calc(5rem+360px+1.5rem)] right-8'
           : 'left-[calc(5rem+2rem)] right-8 lg:right-auto lg:w-[calc((100%-5rem-4rem)/2-1rem)]',
       )}
       style={{