🤖 Fix ImageMagick installation: cache Homebrew downloads only

Changed strategy:
- Cache ~/Library/Caches/Homebrew (download cache) instead of Cellar
- Let 'brew install imagemagick' run every time (fast with cached downloads)
- This ensures proper symlinks in /opt/homebrew/bin
- With Depot's 10x faster cache, downloads will be instant

Previous approach tried to cache the installed package but that doesn't
create PATH symlinks, causing 'magick: command not found' errors.

Author: ammar-agent

.github/actions/setup-cmux/action.yml

@@ -20,13 +20,10 @@ runs:
       if: runner.os == 'macOS'
       uses: actions/cache@v4
       with:
-        path: |
-          ~/Library/Caches/Homebrew
-          /usr/local/Cellar/imagemagick
-          /opt/homebrew/Cellar/imagemagick
-        key: ${{ runner.os }}-brew-imagemagick-7.1
+        path: ~/Library/Caches/Homebrew
+        key: ${{ runner.os }}-brew-cache-${{ hashFiles('**/bun.lock') }}
         restore-keys: |
-          ${{ runner.os }}-brew-imagemagick-
+          ${{ runner.os }}-brew-cache-
 
     - name: Install dependencies
       shell: bash
@@ -36,12 +33,16 @@ runs:
       if: runner.os == 'macOS'
       shell: bash
       run: |
-        if ! command -v magick &> /dev/null && ! command -v convert &> /dev/null; then
-          echo "Installing ImageMagick..."
-          brew install imagemagick
+        if ! brew list imagemagick &>/dev/null; then
+          echo "📦 Installing ImageMagick..."
+          time brew install imagemagick
         else
-          echo "ImageMagick already installed (cached)"
+          echo "✅ ImageMagick already installed"
+          brew list imagemagick --versions
         fi
+        # Verify it's in PATH
+        which magick
+        magick --version | head -1
 
     - name: Install ImageMagick (Linux)
       if: runner.os == 'Linux'