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>

.github/workflows/ci.yml

@@ -0,0 +1,110 @@
+name: CI
+
+on:
+  push:
+    branches: [ main, develop ]
+  pull_request:
+    branches: [ main ]
+
+env:
+  CARGO_TERM_COLOR: always
+  RUST_BACKTRACE: 1
+
+jobs:
+  # ── Native builds: Windows, macOS, Linux ────────────────────────────────────
+  native:
+    name: Native — ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-latest
+            target: x86_64-unknown-linux-gnu
+          - os: windows-latest
+            target: x86_64-pc-windows-msvc
+          - os: macos-latest
+            target: aarch64-apple-darwin
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: ${{ matrix.target }}
+
+      - name: Cache Cargo registry and build
+        uses: Swatinem/rust-cache@v2
+
+      # Linux: install Bevy's system dependencies (X11, Wayland, audio)
+      - name: Install Linux system dependencies
+        if: matrix.os == 'ubuntu-latest'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            libasound2-dev \
+            libudev-dev \
+            libwayland-dev \
+            libxkbcommon-dev \
+            libx11-dev \
+            libxi-dev \
+            pkg-config
+
+      - name: Check (fast compile check)
+        run: cargo check --workspace --target ${{ matrix.target }}
+
+      - name: Build (debug)
+        run: cargo build --workspace --target ${{ matrix.target }}
+
+      - name: Run tests
+        run: cargo test --workspace --target ${{ matrix.target }}
+
+      - name: Clippy
+        run: cargo clippy --workspace --target ${{ matrix.target }} -- -D warnings
+
+  # ── WASM / Web build ─────────────────────────────────────────────────────────
+  wasm:
+    name: WASM — Web
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain + WASM target
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: wasm32-unknown-unknown
+
+      - name: Cache Cargo
+        uses: Swatinem/rust-cache@v2
+
+      - name: Install Trunk
+        uses: jetli/trunk-action@v0.5.0
+
+      - name: Check WASM compile
+        run: >
+          cargo check
+          --target wasm32-unknown-unknown
+          -p sylpheed-viewer
+          -p sylpheed-formats
+
+      - name: Build WASM release with Trunk
+        run: trunk build --release
+
+      - name: Upload WASM dist artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: web-dist
+          path: dist/
+
+  # ── Format check ─────────────────────────────────────────────────────────────
+  fmt:
+    name: Formatting
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+      - run: cargo fmt --all -- --check