docs: add full wiki with 74 pages, assets, and CI workflow

Adds the complete TREK documentation wiki covering installation,
trip planning, admin panel, MCP/AI integration, addons, and operations.

Also fixes encrypt-at-rest gaps: mapbox_access_token, Synology
credentials, per-user webhook/ntfy tokens, and photo passphrases
are now rotated by migrate-encryption.ts and stored encrypted via
settingsService.

wiki/Display-Settings.md

@@ -0,0 +1,56 @@
+# Display Settings
+
+The Display tab (Settings → Display) controls the visual appearance and locale preferences of the app. All changes save immediately to your account and persist across devices.
+
+<!-- TODO: screenshot: appearance settings panel -->
+
+![Display Settings](assets/UsrSettings.png)
+
+## Color mode
+
+Choose between three options:
+
+| Option | Behaviour |
+|--------|-----------|
+| Light | Always uses the light theme |
+| Dark | Always uses the dark theme |
+| Auto | Follows your operating system / browser preference |
+
+## Language
+
+Select your preferred language from the button grid (desktop) or dropdown (mobile). The change takes effect immediately without a page reload. See [Languages](Languages) for the full list of supported languages.
+
+## Temperature unit
+
+Affects the weather widget on trip days.
+
+| Option | Display |
+|--------|---------|
+| °C Celsius | Metric |
+| °F Fahrenheit | Imperial |
+
+## Time format
+
+Affects all time displays throughout the app.
+
+| Option | Example |
+|--------|---------|
+| 24h | 14:30 |
+| 12h | 2:30 PM |
+
+## Route calculation
+
+Toggles automatic route calculation between places on the trip map. Set to **On** or **Off**.
+
+## Booking route labels
+
+Shows or hides labels on booking-related route segments on the map. Set to **On** or **Off**.
+
+## Blur booking codes
+
+When enabled, confirmation codes and reference numbers are blurred until you hover or tap. Set to **On** or **Off**.
+
+## See also
+
+- [Languages](Languages)
+- [User-Settings](User-Settings)