Add syntax highlighting, OSD, search, perf optimizations, and UX improvements

- troika-three-text MSDF rendering for resolution-independent code text
- highlight.js syntax highlighting with Catppuccin Mocha colors
- Lazy text pool: max 25 concurrent code meshes, created on demand
- LOD throttled to every 3 frames, OSD every 10
- 45° tiled watermark (repo/path/filename) behind code
- OSD: breadcrumb, file stats, zoom level
- Search: / or Ctrl+F to find and fly to files
- Keybindings: WASD pan, Q/E rotate, Z/C zoom, Space overview, ? help modal
- Mouse wheel zoom vs trackpad pan detection via event frequency
- Zip GBK filename encoding fallback for Chinese filenames
- Docker volume persistence for SQLite cache

server/Cargo.toml

@@ -14,6 +14,7 @@ walkdir = "2"
 sha2 = "0.10"
 hex = "0.4"
 zip = "2"
+encoding_rs = "0.8"
 tempfile = "3"
 tracing = "0.1"
 tracing-subscriber = "0.3"