feat: add ENABLE_UPDATE_CHECKS and migrate ETag storage to database (#…

…707)

* feat: add ENABLE_UPDATE_CHECKS and migrate ETag storage to database

- Add ENABLE_UPDATE_CHECKS configuration option (defaulting to "1")
- Disable update checks globally in tests to avoid GitHub API rate limits
- Refactor firmware downloader to store ETag in the database settings instead of a local file
- use ETag for system update checks

deps: bump pixlet

deps: bump deps

feat: send custom firmware files to devices

fix: handle device deletion gracefully in UI (#671)

Redirects to the home page instead of reloading if the current page belongs to the deleted device, preventing 404 errors when a device is deleted.

fix: Support .webp-only apps in user library

- Update scanUserAppsDir to detect apps defined by a single .webp file.
- Update RenderApp to return file content directly for .webp apps.
- Skip schema generation in handleConfigAppGet for .webp apps to prevent errors.

docs: add ID-only update pattern to GEMINI.md as a best practice

Refactor AutoPin logic and add comprehensive tests

- Extracted AutoPin logic into a reusable handleAutoPin helper in internal/server/render_utils.go.
- Enabled AutoPin support for pushed apps in possiblyRender, ensuring consistent behavior across app types.
- Added TestDetermineNextApp_AutoPin to internal/server/rotation_test.go to verify auto-pinning on success and auto-unpinning on failure.

feat: only show OTA if HTTPS is used

This is because the device uses the ESP HTTPS OTA
(https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/system/esp_https_ota.html#esp-https-ota)
which requires HTTPS.