docs: add mdBook docs-site, publish workflow, and release-notes tooling

Add a docs-site (mdBook) with a Gitea publish-docs workflow, a
release-notes generator script (release:notes) that turns a commit
range's TRACES into grouped notes, the background-audio feature spec,
and CLAUDE.md. Ignore docs-site build artifacts.

.gitea/workflows/publish-docs.yml

@@ -0,0 +1,125 @@
+name: Publish Documentation
+
+# Renders the markdown docs (docs/*.md) into an mdBook site, builds the Rust
+# API reference with cargo doc, and force-pushes the combined output to the
+# orphan `gitea-pages` branch that the Gitea Pages server serves.
+#
+# The published matrix is regenerated during the build, so it is never stale.
+
+on:
+  push:
+    branches:
+      - master
+
+concurrency:
+  # Only one docs publish at a time; a newer push supersedes an in-flight run.
+  group: publish-docs
+  cancel-in-progress: true
+
+jobs:
+  publish-docs:
+    name: Build & publish docs to gitea-pages
+    runs-on: linux/amd64
+    container:
+      image: gitea.tourolle.paris/dtourolle/jellytau-builder:latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v1
+        with:
+          bun-version: latest
+
+      - name: Install dependencies
+        run: bun install
+
+      - name: Install mdBook
+        run: |
+          set -e
+          MDBOOK_VERSION=v0.4.40
+          URL="https://github.com/rust-lang/mdBook/releases/download/${MDBOOK_VERSION}/mdbook-${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz"
+          echo "⬇️  Downloading mdBook ${MDBOOK_VERSION}"
+          curl -fsSL "$URL" | tar -xz -C /usr/local/bin
+          mdbook --version
+
+      - name: Regenerate traceability matrix (keep published copy current)
+        run: bun run traces:markdown
+
+      - name: Assemble mdBook sources
+        run: |
+          set -e
+          # mdBook's src is docs/. Drop in the SUMMARY and the generated
+          # intro + API redirect pages (build artifacts, not committed).
+          cp docs-site/SUMMARY.md docs/SUMMARY.md
+
+          cat > docs/README.md <<'EOF'
+          # JellyTau Documentation
+
+          Cross-platform Jellyfin client — business logic in a Rust backend,
+          SvelteKit + TypeScript frontend, talking over Tauri v2 IPC.
+
+          - **[Requirements Specification](requirements.md)** — user, integration, and development requirements.
+          - **[Traceability Matrix](traceability.md)** — generated map from requirements to code (regenerated on every publish).
+          - **[Architecture](architecture/README.md)** — backend, frontend, data flow, platform backends.
+          - **[Rust API Reference](api/index.html)** — rustdoc for the `src-tauri` backend.
+
+          _This site is published automatically from `master` by the `publish-docs` CI job._
+          EOF
+
+          cat > docs/api-redirect.md <<'EOF'
+          # Rust API Reference
+
+          The full backend API reference is generated by `cargo doc` (rustdoc).
+
+          👉 **[Open the Rust API Reference](api/index.html)**
+          EOF
+
+      - name: Build mdBook site
+        run: mdbook build docs-site --dest-dir "$GITHUB_WORKSPACE/site"
+
+      - name: Build Rust API docs (cargo doc)
+        working-directory: src-tauri
+        # --no-deps keeps it to our own crate (fast, focused); document private
+        # items so internal modules/commands appear.
+        run: |
+          cargo doc --no-deps --document-private-items
+          # The backend modules/commands live in the LIB crate (jellytau_lib);
+          # the bin crate (jellytau) is a near-empty shim. Land on the lib.
+          echo '<meta http-equiv="refresh" content="0; url=jellytau_lib/index.html">' \
+            > target/doc/index.html
+
+      - name: Assemble published output
+        run: |
+          set -e
+          mkdir -p "$GITHUB_WORKSPACE/site/api"
+          cp -r src-tauri/target/doc/. "$GITHUB_WORKSPACE/site/api/"
+          # Disable Jekyll processing on the pages branch.
+          touch "$GITHUB_WORKSPACE/site/.nojekyll"
+          ls -la "$GITHUB_WORKSPACE/site"
+
+      - name: Push to gitea-pages branch
+        env:
+          # PAT preferred; falls back to the auto-provided token (same pattern
+          # as build-release.yml).
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+          AUTO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -e
+          TOKEN="${GITEA_TOKEN:-$AUTO_TOKEN}"
+          REPO="${GITHUB_REPOSITORY}"
+          HOST="$(echo "$GITHUB_SERVER_URL" | sed -E 's#^https?://##')"
+          REMOTE="https://oauth2:${TOKEN}@${HOST}/${REPO}.git"
+
+          cd "$GITHUB_WORKSPACE/site"
+          git init -q
+          git config user.name "gitea-actions"
+          git config user.email "actions@gitea.tourolle.paris"
+          git checkout -q -b gitea-pages
+          git add -A
+          git commit -q -m "docs: publish site from ${GITHUB_SHA::8}"
+          echo "🚀 Force-pushing to gitea-pages"
+          git push -f "$REMOTE" gitea-pages