Fix desktop settings misclassification in pywebview

[mot-yelraf]

Summary

A wide desktop window could receive phone-style settings when the browser reported a small screen width. Require a valid phone-sized screen and coarse pointer for the screen-width fallback, keeping JavaScript and CSS aligned while preserving compact settings for narrow windows.

Adds desktop regression coverage for General, Sensor, and Switch Settings, documents the layout rules, and updates the version to v0.26.259.1.

Verification

• npm run validate:pr: 33 Chromium tests passed on macOS with Python 3.13.9, including phone navigation, saving, resizing, and desktop settings.
• The new 600px-screen regression failed against the original assets and passed with the fix.
• Native pywebview checks against an isolated fixture passed for all three settings dialogs on Raspberry Pi Bookworm and both Trixie hosts. No production settings were saved or services restarted.
• User verified desktop and mobile Web UI behavior.
• git diff --check: passed.
• No MQTT broker or direct sensor/relay hardware was needed for this UI-only change.

Contributor checklist

• This pull request is focused on one logical change.
• I added or updated tests for behavior changes.
• I updated the canonical documentation when behavior or configuration changed.
• I did not commit credentials, private runtime configuration, databases, or logs.
• I preserved compatibility-sensitive MQTT, settings, switch identity, and persistence behavior, or documented an intentional break.

Maintainer verification

• Required remote checks pass (Python 3.11/3.13 compile and the full regression suite with coverage floor).
• npm run validate:pr passes on a trusted host when the change can affect rendered UI behavior.
• Hardware-, broker-, onboarding-, and platform-specific behavior not covered remotely is recorded below.

Residual risk or unverified areas

The original long-running desktop session's failure was not reproduced in fresh native windows. The screen-width misclassification path was reproduced in Chromium and fixed; the user subsequently verified desktop and mobile Web UI behavior. Hardware control, MQTT, and onboarding were not exercised because their behavior is unchanged.