Add Docker support to smoke test, add inject-wifi.sh

Smoke test improvements:
- Add --docker flag for testing Docker containers
- Skip SSH/systemd checks in Docker mode
- Docker health check verifies HTTP response
- Show "Docker Smoke Test" header in Docker mode

inject-wifi.sh:
- Add to repo (was gitignored)
- Add cleanup trap for robustness
- Supports NetworkManager (Bookworm) and wpa_supplicant (legacy)

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

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

.gitignore

@@ -70,7 +70,6 @@ scripts/
 # Web UI auth database and SSL certs
 frontends/web/instance/
 frontends/web/certs/
-rpi/inject-wifi.sh
 
 # RPi image build artifacts
 *.img