Implement Cast Streaming mirroring, DLNA casting, daemon+GUI, and breadd integration

Builds out the full v1 scope: a vendored+patched openscreen subset for
low-latency Cast Streaming (Mirroring receiver 0F5096E8) alongside the
existing Cast V2/HLS and new DLNA/AVTransport casting paths, breadcastd's
Idle/Casting state machine with a private IPC socket, the breadcast GTK4
popup as a thin IPC client, and bread.cast.*/bread.command.cast.* breadd
integration (device discovery, start/stop, mirroring lifecycle events).
Also adds bakery/systemd/Forgejo CI packaging.

Validated end-to-end against a real Chromecast/Google TV: negotiated
Cast Streaming session, live pipeline playback, and daemon+GUI click-to-cast/
stop through the actual popup.

.forgejo/workflows/dev-release.yml

@@ -0,0 +1,79 @@
+name: dev release
+
+# Publishes a dev-track build on every push to `dev` —
+# separate from release.yml's tag-triggered stable releases. See
+# bread-ecosystem's docs/release-channels.md for the three-track policy
+# this is part of.
+on:
+  push:
+    branches: ['dev']
+
+jobs:
+  build:
+    runs-on: [self-hosted, hestia]
+    steps:
+      - name: checkout
+        run: |
+          set -euo pipefail
+          rm -rf src && mkdir src
+          git clone --branch dev --depth 1 \
+            "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" src
+
+      - name: build
+        run: cd src && cargo build --release --locked
+
+      - name: compute dev version
+        run: |
+          set -euo pipefail
+          cd src
+          # Base the dev version off the latest published stable tag,
+          # not Cargo.toml — Cargo.toml can go stale relative to the last
+          # real release (seen in practice: breadbox/breadpad/breadcrumbs/
+          # breadpaper), which would make a dev build sort as OLDER than
+          # what's already installed and bakery would correctly refuse it.
+          LATEST_TAG="$(git ls-remote --tags --refs \
+            "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" 'v*' \
+            | awk -F/ '{print $NF}' | sed 's/^v//' | sort -V | tail -1)"
+          if [ -n "${LATEST_TAG}" ]; then
+            CUR="${LATEST_TAG}"
+          else
+            CUR="$(grep -m1 '^version' breadcast/Cargo.toml | sed -E 's/.*"(.*)".*/\1/')"
+          fi
+          IFS='.' read -r MA MI PA <<< "${CUR}"
+          SHA="$(git rev-parse --short HEAD)"
+          TS="$(date -u +%Y%m%d%H%M%S)"
+          echo "VERSION=${MA}.${MI}.$((PA + 1))-dev.${TS}+${SHA}" >> "$GITHUB_ENV"
+
+      - name: prepare artifacts
+        run: |
+          set -euo pipefail
+          PKG_DIR="/srv/breadway-dl/dev/breadcast/${VERSION}"
+          mkdir -p "${PKG_DIR}"
+          for bin in breadcast breadcastd; do
+            cp "src/target/release/${bin}" "${PKG_DIR}/${bin}-x86_64"
+            strip "${PKG_DIR}/${bin}-x86_64"
+            sha256sum "${PKG_DIR}/${bin}-x86_64" | awk '{print $1}' \
+              > "${PKG_DIR}/${bin}-x86_64.sha256"
+          done
+          cp src/contrib/breadcastd.service "${PKG_DIR}/"
+          cp src/bakery.toml "${PKG_DIR}/bakery.toml"
+          ln -sfn "${VERSION}" "/srv/breadway-dl/dev/breadcast/latest"
+
+      # No GitHub Release upload — dev, like the other non-stable track,
+      # is only distributed via dl.breadway.dev/dev/.
+      - name: regenerate dev index.json
+        env:
+          MINISIGN_SEC_KEY: ${{ secrets.BAKERY_MINISIGN_SEC_KEY_PATH }}
+        run: |
+          set -euo pipefail
+          if [ -z "${MINISIGN_SEC_KEY:-}" ]; then
+            echo "::error::BAKERY_MINISIGN_SEC_KEY_PATH secret not set — refusing to regenerate dev index.json unsigned (would leave a stale signature mismatched against fresh content and break bakery for everyone on the dev track)"
+            exit 1
+          fi
+          rm -rf /tmp/bread-ecosystem-ci-* 2>/dev/null || true
+          # mktemp: a fixed clone path races when multiple repos' dev/beta
+          # workflows run close together on the same self-hosted runner.
+          ECOSYSTEM_CI_DIR="$(mktemp -d /tmp/bread-ecosystem-ci-XXXXXX)"
+          git clone --branch dev https://git.breadway.dev/Breadway/bread-ecosystem.git "${ECOSYSTEM_CI_DIR}"
+          TRACK=dev bash "${ECOSYSTEM_CI_DIR}/scripts/gen-index.sh"
+          rm -rf "${ECOSYSTEM_CI_DIR}"