Patch chromium flag endpoint

[hiroTamada]

Here's a PR description for your changes:

---

Add Dynamic Chromium Flags API & Refactor Restart Logic

This PR adds the ability to dynamically update Chromium launch flags at runtime and consolidates duplicate code across the codebase.

Changes

New Feature:

• Added PATCH /chromium/flags endpoint to update Chromium flags dynamically without container restart
• Updated run-docker.sh to make flags file writable (removed ro mount option)
• Set default to --kiosk mode for better fullscreen experience

Code Refactoring:

• Created mergeAndWriteChromiumFlags() helper to consolidate flag merging logic (eliminates 52 lines of duplication)
• Created restartChromiumAndWait() helper to consolidate Chromium restart logic (eliminates 62 lines of duplication)
• Removed duplicate restartChromium() function from display.go
• Updated display resolution handlers to use shared restart helper

Benefits:

• Single source of truth for Chromium restart and flag management
• Better logging with operation-specific context
• Consistent error handling across all Chromium operations
• ~100 lines of code reduction through DRY principles

Testing

E2E Tests:

• Ran TestExtensionUploadAndActivation in e2e_chromium_test.go to verify extension endpoint still works correctly

Manual Testing:

• Started Docker container with the updated image
• Called the new flags endpoint to enable kiosk mode:

  curl -X PATCH http://localhost:444/chromium/flags \
    -H "Content-Type: application/json" \
    -d '{"flags": ["--kiosk"]}'

• Verified kiosk mode was successfully applied and Chromium restarted with new flags

Unit Tests:

• Added TestApiService_PatchChromiumFlags to verify flag validation and merging logic
• All existing tests pass

---

Note

Introduces a new PATCH /chromium/flags API and consolidates Chromium flag merging and restart logic into shared helpers, updating extension upload and display flows, with OpenAPI/client generation and a unit test.

• API/OpenAPI:
  • Add PATCH /chromium/flags endpoint (request: { flags: string[] }; responses: 200/400/500).
  • Regenerate oapi client/server types, routing, and swagger spec for the new endpoint.
• Backend:
  • Implement ApiService.PatchChromiumFlags to validate, merge, write flags, restart Chromium, and wait for DevTools.
  • Refactor into helpers: mergeAndWriteChromiumFlags() and restartChromiumAndWait().
  • Update UploadExtensionsAndRestart to use the new helpers and improved logging.
  • Remove old restartChromium() from display.go and replace calls with restartChromiumAndWait().
• Tests:
  • Add TestApiService_PatchChromiumFlags covering flag validation/flow.

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[hiroTamada]

As @rgarcia mentioned, when a user is request extension and kiosk. We are restarting the chromium twice.
This pr does not include a fix for it. Instead, I consolidated the paths/functions around restarting chromium and updating chromium flags.

https://linear.app/onkernel/issue/KERNEL-426/avoid-redundant-chromium-restart-with-kiosk-and-extension-enabled

I created a ticket for this as a backlog