feat(phase3): PWA, auto-discovery, bookmarklet, multi-tab sync

- PWA: manifest, service worker (cache-first static, network-first API),
  offline page, install prompt banner
- Auto-discovery: Docker socket + Traefik API scanning, approval UI
- Quick-add bookmarklet: popup-based add page, favicon auto-detect
- Multi-tab sync: BroadcastChannel for theme + data changes
- i18n translations for all new strings (EN/RU)

src/lib/stores/theme.svelte.ts

@@ -1,3 +1,5 @@
+import { broadcastThemeChange } from '$lib/utils/broadcastSync.js';
+
 const THEME_STORAGE_KEY = 'wal-theme-mode';
 const PRIMARY_HUE_KEY = 'wal-primary-hue';
 const PRIMARY_SAT_KEY = 'wal-primary-sat';
@@ -36,6 +38,7 @@ class ThemeStore {
 	backgroundType = $state<BackgroundType>('mesh');
 
 	#systemPreference: 'dark' | 'light' = 'dark';
+	#suppressBroadcast = false;
 
 	resolvedMode = $derived<'dark' | 'light'>(
 		this.mode === 'system' ? this.#systemPreference : this.mode
@@ -98,6 +101,20 @@ class ThemeStore {
 			html.style.setProperty('--primary-h', String(this.primaryHue));
 			html.style.setProperty('--primary-s', `${this.primarySaturation}%`);
 		});
+
+		// Broadcast theme changes to other tabs
+		$effect(() => {
+			// Read all reactive values to track them
+			const snapshot = {
+				mode: this.mode,
+				primaryHue: this.primaryHue,
+				primarySaturation: this.primarySaturation,
+				backgroundType: this.backgroundType
+			};
+			if (typeof window === 'undefined') return;
+			if (this.#suppressBroadcast) return;
+			broadcastThemeChange(snapshot);
+		});
 	}
 
 	cycleMode() {
@@ -119,6 +136,27 @@ class ThemeStore {
 		this.primarySaturation = Math.max(0, Math.min(100, saturation));
 	}
 
+	/**
+	 * Apply theme values received from another tab via BroadcastChannel.
+	 * Suppresses re-broadcasting to avoid echo loops.
+	 */
+	applyFromBroadcast(values: {
+		mode: ThemeMode;
+		primaryHue: number;
+		primarySaturation: number;
+		backgroundType: BackgroundType;
+	}) {
+		this.#suppressBroadcast = true;
+		this.mode = values.mode;
+		this.primaryHue = values.primaryHue;
+		this.primarySaturation = values.primarySaturation;
+		this.backgroundType = values.backgroundType;
+		// Re-enable on next microtask so the effect reads suppressBroadcast=true
+		queueMicrotask(() => {
+			this.#suppressBroadcast = false;
+		});
+	}
+
 	/**
 	 * Apply non-null server-stored user preferences over localStorage defaults.
 	 * Call from +layout.svelte when user data is available.