ci: add experimental companion firmware build workflow

Triggers on tags matching companion-experimental-* pushed from the
font-experiments branch. Appends -experimental to the version string
so all output filenames are clearly distinguishable from stable builds.
Creates a separate draft release labeled "(Experimental)".

Usage: git tag companion-experimental-v1.x.x && git push origin companion-experimental-v1.x.x

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

.github/workflows/build-companion-experimental-firmwares.yml

@@ -0,0 +1,42 @@
+name: Build Experimental Companion Firmwares
+
+permissions:
+  contents: write
+
+on:
+  workflow_dispatch:
+  push:
+    tags:
+      - 'companion-experimental-*'
+
+jobs:
+
+  build:
+    runs-on: ubuntu-latest
+    steps:
+
+      - name: Clone Repo
+        uses: actions/checkout@v4
+
+      - name: Setup Build Environment
+        uses: ./.github/actions/setup-build-environment
+
+      - name: Build Firmwares
+        env:
+          FIRMWARE_VERSION: ${{ env.GIT_TAG_VERSION }}-experimental
+        run: /usr/bin/env bash build.sh build-companion-firmwares
+
+      - name: Upload Workflow Artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: companion-firmwares-experimental
+          path: out
+
+      - name: Create Release
+        uses: softprops/action-gh-release@v2
+        if: startsWith(github.ref, 'refs/tags/')
+        with:
+          name: Companion Firmware ${{ env.GIT_TAG_VERSION }} (Experimental)
+          body: "Experimental build from the font-experiments branch. Includes extended Lemon font with native Greek and Cyrillic rendering."
+          draft: true
+          files: out/*