P2: Support Deep UI Pattern Parity (Bottom Sheets, Context Menus)

[vriesdemichael]

Following the UI paradigms outlined in ui-patterns.md, we need to adapt desktop UI patterns to their React Native equivalents.

Required Patterns

1. Interactive Context Menus: Using Long-Press or Swipe Actions for actions like Rename Session, Compact, or Delete instead of desktop right-click menus.
2. Bottom Sheets for Complex Dialogs: Modals like settings or AI provider configurations should fly up as native Bottom Sheets rather than center web-style modals.
3. Split Panes to Stacks: The desktop side-by-side (Sidebar + Main Content) layout is already largely migrated to standard mobile Navigation Stacks, but any nested split panes (like the prompt context window vs the chat timeline) must be resolved to native mobile overlaps (like KeyboardAvoidingView + absolute positioning).