#6255: fix(media): expand ~ in CLI command paths

## Summary Expands `~` in CLI media model command paths before execution. The `command` field in CLI media model configs was not expanding `~` before execution. Since `execFile` doesn't process shell expansions, paths like `~/.openclaw/skills/...` would fail with ENOENT. Now calls `expandHomeDir()` on the command path. **Note:** The audio text extraction fix that was originally part of this PR has already been merged separately into main. ## Test plan - [ ] Configure a CLI media model with `~` in the command path - [ ] Verify media understanding works without ENOENT errors --- 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>