feat: initialise workspace — Milestone 1 asset explorer

Three-crate Cargo workspace structured per PROJECT.md spec:
- crates/sylpheed-formats  — Xbox 360 format parsers (no Bevy)
- crates/sylpheed-viewer   — Bevy 0.15 asset viewer + egui UI
- crates/sylpheed-cli      — CLI tools (extract/list/sniff/texture)

Milestone 1 features:
- XISO disc image reading via xdvdfs 0.8
- XPR2 texture container parsing + Morton de-tiling
- D3DFORMAT → wgpu TextureFormat mapping (DXT1/3/5, DXN, ARGB)
- Custom Bevy AssetLoader for .xpr files
- Orbit camera (LMB orbit, RMB pan, scroll zoom)
- egui file browser + RE notes panel
- CLI: extract / list / sniff / texture info / texture export
- GitHub Actions CI (Linux, macOS, Windows, WASM)
- Trunk WASM build config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,22 @@
+# Rust build artifacts
+/target/
+**/target/
+/dist/
+
+# Extracted game assets — never commit these
+assets/
+*.iso
+*.xiso
+
+# IDE / OS
+.idea/
+.vscode/
+*.swp
+.DS_Store
+Thumbs.db
+
+# Local dev overrides
+.env
+
+# Trunk build output
+dist/