Detailed Description
ActivityStack manages a stack of Activity widgets, providing Android-style navigation where activities can be pushed onto the stack and popped via back navigation.
Features:
- Push/pop navigation with transition animations
- Activity lifecycle management (onResume/onPause callbacks)
- Optional header bar with back button
- Activity registration and lookup by name
- Back stack helpers (popTo, clearAndPush, isOnStack)
- Per-activity custom headers via ActivityHeader interface
- Header managed externally by OverlayHeaderLayout
