Enhance SPA list interactions with Shift+Click and Mobile Drag

[google-labs-jules]

Implemented enhanced selection interactions for the SPA:

1. Shift+Click Range Selection: Users can now select a range of items in the Search Results or Course Group Candidates lists by holding Shift. The logic anchors to the last clicked item and syncs the range to the target state.
2. Mobile Drag Selection:
   • Long-press (500ms) on an item activates drag mode.
   • Dragging up/down selects items in real-time.
   • Auto-scrolling activates when dragging near the top/bottom edges of the screen/container.
   • Visual feedback (ripple animation) indicates activation.
3. Sticky Headers: The App Header and Navigation Tabs now stick to the top of the viewport.
4. Optimizations: Disabled text selection on list items during interactions.

Verified with Playwright tests (verification/verify_interaction.py).

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PR created automatically by Jules for task 11246814939022537362 started by @OsakaLOOP

[google-labs-jules]

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