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.lock

@@ -900,6 +900,7 @@ name = "repo-vis-server"
 version = "0.1.0"
 dependencies = [
  "axum",
+ "encoding_rs",
  "hex",
  "rusqlite",
  "serde",