fix: add ffmpeg and ttyd as dependencies in homebrew cask

Users installing via homebrew cask were missing required dependencies.
This adds ffmpeg and ttyd as formula dependencies to ensure they are
automatically installed when users run 'brew install agentstation/tap/vhs'.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: jackspirou

.goreleaser.yaml

@@ -152,6 +152,10 @@ homebrew_casks:
 
     name: vhs
 
+    dependencies:
+      - formula: ffmpeg
+      - formula: ttyd
+    
     directory: Casks
 
     commit_author: