bakery: add stable/beta/dev build tracks

Adds a track concept to bakery (separate from the existing bakery/pacman
distribution channel): stable (unchanged tag-triggered releases), beta
(deliberate beta-v* tag promotion), and dev (published on every push to
dev). Each track gets its own signed index + artifact tree under
dl.breadway.dev so stable's paths and existing installs are untouched.

- bakery: new Track type, a global track preference in installed.json
  (defaults to stable via serde, no migration needed), `bakery track
  show`/`set`, a BAKERY_INDEX_BASE_URL override for testing, and a real
  semver comparison in `update` (was a plain string-equality check before).
  ANSI-colored/aligned CLI output (TTY + NO_COLOR aware).
- gen-index.sh: TRACK env var selects which subtree to read/write.
- CI: dev-bakery.yml/beta-bakery.yml/dev-bread-theme.yml/beta-bread-theme.yml
  publish those two products on the new tracks; dev/beta skip the GitHub
  Release upload step (no per-commit release spam).
- docs/release-channels.md documents the three-track policy.

.forgejo/workflows/beta-bread-theme.yml

@@ -0,0 +1,56 @@
+name: beta bread-theme
+
+# Publishes a beta-track build when a `beta-v*` tag is pushed — a deliberate
+# promotion step, distinct from dev-bread-theme.yml's build-on-every-push.
+# See docs/release-channels.md.
+on:
+  push:
+    tags: ['beta-v*']
+
+jobs:
+  build:
+    runs-on: [self-hosted, hestia]
+    steps:
+      - name: checkout
+        run: |
+          set -euo pipefail
+          rm -rf src && mkdir src
+          git clone --branch "${GITHUB_REF_NAME}" --depth 1 \
+            "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" src
+
+      - name: build
+        run: cd src && cargo build --release --locked -p bread-theme --bin bread-theme
+
+      - name: prepare artifacts
+        run: |
+          set -euo pipefail
+          VERSION="${GITHUB_REF_NAME#beta-v}"
+          PKG_DIR="/srv/breadway-dl/beta/bread-theme/${VERSION}"
+          mkdir -p "${PKG_DIR}"
+          cp "src/target/release/bread-theme" "${PKG_DIR}/bread-theme-x86_64"
+          strip "${PKG_DIR}/bread-theme-x86_64"
+          sha256sum "${PKG_DIR}/bread-theme-x86_64" | awk '{print $1}' \
+            > "${PKG_DIR}/bread-theme-x86_64.sha256"
+          cp src/bread-theme/bakery.toml "${PKG_DIR}/bakery.toml"
+          ln -sfn "${VERSION}" "/srv/breadway-dl/beta/bread-theme/latest"
+
+      - name: sign beta binary
+        env:
+          MINISIGN_SEC_KEY: ${{ secrets.BAKERY_MINISIGN_SEC_KEY_PATH }}
+        run: |
+          set -euo pipefail
+          VERSION="${GITHUB_REF_NAME#beta-v}"
+          PKG_DIR="/srv/breadway-dl/beta/bread-theme/${VERSION}"
+          if [ -n "${MINISIGN_SEC_KEY:-}" ]; then
+            minisign -W -S -s "${MINISIGN_SEC_KEY}" -m "${PKG_DIR}/bread-theme-x86_64" \
+              -x "${PKG_DIR}/bread-theme-x86_64.minisig" </dev/null
+            echo "signed bread-theme-x86_64"
+          else
+            echo "::warning::BAKERY_MINISIGN_SEC_KEY_PATH not set — shipping bread-theme-x86_64 UNSIGNED"
+          fi
+
+      - name: regenerate beta index.json
+        env:
+          MINISIGN_SEC_KEY: ${{ secrets.BAKERY_MINISIGN_SEC_KEY_PATH }}
+          TRACK: beta
+        run: cd src && bash scripts/gen-index.sh