feat(v0.501): Sprint 4 -- Cloud frontend + Gear advanced
- C1-09: Create CloudPage with folder tree, file list, and /cloud route
- C1-10: Create CloudUploadModal with drag-and-drop and progress
- C1-11: Create CloudFilePreview mini player inline
- C1-12: Add Cloud stories (loading, empty, populated, quota full)
- G1-01: Add is_public toggle, public gear endpoint, GearShowcase
- G1-02: Add gear image upload endpoints, GearImageGallery component
- G1-03: Add gear search with ILIKE + SearchBar in toolbar
- G1-04: Add stories for GearShowcase and GearImageGallery
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