Replace 4 independent position:fixed elements with one flex container that
stacks them naturally from bottom to top. Elements push each other
automatically — no more hardcoded offsets or z-index conflicts.
Stack order (bottom → top):
1. PillNavigation (collapsible)
2. TagStrip (togglable)
3. QuickInputBar + toggle button row
Shared-UI changes:
- PillNavigation: add positioning='fixed'|'static' prop
- QuickInputBar: add positioning='fixed'|'static' prop
- TagStrip: add positioning='fixed'|'static' prop
- All default to 'fixed' for backward compatibility
Layout changes:
- Wrap all bottom elements in .bottom-stack (position:fixed, flex-column)
- Remove hardcoded bottomOffset calculations
- Toggle button is now inline next to QuickInputBar (not separately positioned)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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