UI: configure settings via URL params

[naltatis]

Addresses #6922

Lets kiosk displays and iframe embeds force UI preferences through the URL instead of relying on browser settings or persisted storage. Params are validated, written to the existing localStorage-backed settings, then stripped from the address bar.

• ?theme=, ?lang=, ?unit=, ?format= applied on boot (e.g. ?theme=dark&lang=de&unit=mi&format=24)
• values persist to localStorage, so a cleared kiosk reapplies them on reload

Todo

• add documentation Add Web UI reference page docs#1096

[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• In app.ts, applyUrlSettings() is called but the function is not imported; add an explicit import from ./urlSettings to avoid runtime/compile errors.
• In urlSettings.ts, consider using the existing setters (e.g. setThemePreference, unit/time-format helpers, locale setter) instead of mutating the settings object directly so that any associated side effects (localStorage writes, DOM updates, reactive state) stay consistent with the rest of the app.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `app.ts`, `applyUrlSettings()` is called but the function is not imported; add an explicit import from `./urlSettings` to avoid runtime/compile errors.
- In `urlSettings.ts`, consider using the existing setters (e.g. `setThemePreference`, unit/time-format helpers, locale setter) instead of mutating the `settings` object directly so that any associated side effects (localStorage writes, DOM updates, reactive state) stay consistent with the rest of the app.

## Individual Comments

### Comment 1
<location path="assets/js/urlSettings.ts" line_range="20" />
<code_context>
+  if (lang === "auto") {
+    settings.locale = null;
+    touched = true;
+  } else if (lang && lang in LOCALES) {
+    settings.locale = lang as keyof typeof LOCALES;
+    touched = true;
</code_context>
<issue_to_address>
**suggestion (bug_risk):** Use a safer own-property check instead of `in` for LOCALES lookup.

`lang in LOCALES` will also match properties on LOCALES’ prototype chain. To ensure only real locale keys are treated as valid, use an own-property check instead, e.g. `Object.prototype.hasOwnProperty.call(LOCALES, lang)` or `Object.hasOwn(LOCALES, lang)` where available.
</issue_to_address>

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