Add Docker support and integrate /convert-to-docker into setup flow

- Update setup skill to detect platform and offer Docker/Apple Container choice
- On Linux, automatically use Docker via /convert-to-docker skill
- On macOS, ask user preference if Apple Container not installed
- Update README to reflect Docker support and Linux compatibility
- Fix exact line number reference in convert-to-docker skill
- Add thank you to @dotsetgreg for the Docker skill contribution

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude/skills/convert-to-docker/SKILL.md

@@ -36,7 +36,7 @@ If Docker is not installed:
 
 Edit `src/container-runner.ts`:
 
-### 1a. Update module comment (line 3)
+### 1a. Update module comment (around line 3)
 
 ```typescript
 // Before: