feat(electrobun): wire persistence — SQLite, 17 themes, font system

Persistence:
- bun:sqlite at ~/.config/agor/settings.db (WAL mode, 500ms busy_timeout)
- 4 tables: schema_version, settings, projects, custom_themes
- 5 RPC handlers: settings.get/set/getAll, projects get/set

Theme system (LIVE switching):
- All 17 themes ported from Tauri (4 Catppuccin + 7 Editor + 6 Deep Dark)
- applyCssVars() sets 26 --ctp-* vars on document.documentElement
- Parallel xterm ITheme mapping per theme
- theme-store.svelte.ts: Svelte 5 rune store, persists to SQLite

Font system:
- font-store.svelte.ts: UI/terminal font family + size
- Live CSS var application (--ui-font-family/size, --term-font-family/size)
- onTermFontChange() callback registry for terminal instances
- Persists all 4 font settings to SQLite

AppearanceSettings wired: 17-theme grouped dropdown, font steppers
Init on startup: restores saved theme + fonts from SQLite

ui-electrobun/src/mainview/theme-store.svelte.ts

@@ -0,0 +1,86 @@
+/**
+ * Svelte 5 rune-based theme store.
+ * Applies all 26 --ctp-* CSS vars to document.documentElement instantly.
+ * Persists selection via settings RPC.
+ *
+ * Usage:
+ *   import { themeStore } from './theme-store.svelte';
+ *   themeStore.setTheme('tokyo-night');
+ *   await themeStore.initTheme(rpc);
+ */
+
+import { applyCssVars, THEME_LIST, type ThemeId } from "./themes.ts";
+
+const SETTING_KEY   = "theme";
+const DEFAULT_THEME: ThemeId = "mocha";
+
+// ── Minimal RPC interface ─────────────────────────────────────────────────────
+// Avoids importing the full Electroview class — just the subset we need.
+
+interface SettingsRpc {
+  request: {
+    "settings.get"(p: { key: string }): Promise<{ value: string | null }>;
+    "settings.set"(p: { key: string; value: string }): Promise<{ ok: boolean }>;
+  };
+}
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function isValidThemeId(id: string): id is ThemeId {
+  return THEME_LIST.some((t) => t.id === id);
+}
+
+// ── Store ─────────────────────────────────────────────────────────────────────
+
+function createThemeStore() {
+  let currentThemeId = $state<ThemeId>(DEFAULT_THEME);
+  let rpc: SettingsRpc | null = null;
+
+  /** Apply CSS vars immediately — synchronous, no flash. */
+  function applyToDocument(id: ThemeId): void {
+    applyCssVars(id);
+    currentThemeId = id;
+  }
+
+  /**
+   * Change the active theme.
+   * Applies CSS vars immediately and persists asynchronously.
+   */
+  function setTheme(id: ThemeId): void {
+    applyToDocument(id);
+    if (rpc) {
+      rpc.request["settings.set"]({ key: SETTING_KEY, value: id }).catch((err) => {
+        console.error("[theme-store] Failed to persist theme:", err);
+      });
+    }
+  }
+
+  /**
+   * Load persisted theme from settings on startup.
+   * Call once in App.svelte onMount.
+   */
+  async function initTheme(rpcInstance: SettingsRpc): Promise<void> {
+    rpc = rpcInstance;
+    try {
+      const result = await rpc.request["settings.get"]({ key: SETTING_KEY });
+      const saved  = result.value;
+      if (saved && isValidThemeId(saved)) {
+        applyToDocument(saved);
+      } else {
+        // Apply default to ensure vars are set even when nothing was persisted.
+        applyToDocument(DEFAULT_THEME);
+      }
+    } catch (err) {
+      console.error("[theme-store] Failed to load theme from settings:", err);
+      applyToDocument(DEFAULT_THEME);
+    }
+  }
+
+  return {
+    get currentTheme() { return currentThemeId; },
+    setTheme,
+    initTheme,
+  };
+}
+
+export const themeStore = createThemeStore();