feat(extension): add Firefox WebExtension support

- Add a neutral WebExtension API adapter that uses Firefox browser.* or Chromium chrome.* without mutating globals.
- Switch extension runtime code to the adapter and add Firefox-specific typings for tabs, windows, tab groups, storage, scripting, and native messaging ports.
- Fix Firefox temporary add-on instructions to load the packaged manifest with background.scripts instead of the Chromium service worker manifest.
- Detect Firefox in clients.list via runtime.getBrowserInfo and keep Chromium user-agent fallback support.
- Make navigate.open wait briefly for Firefox to replace initial about:blank with the requested URL.
- Add JS coverage for API selection, clients.list browser detection, and Firefox navigate.open URL polling.
- Bump package and extension version to 0.15.2.

extension/src/core/storage.ts

@@ -1,8 +1,9 @@
-// chrome.storage.local accessors for profile alias, window aliases, and sessions.
+import { webExtApi as api } from '../browser-api';
+// api.storage.local accessors for profile alias, window aliases, and sessions.
 import type { SessionTab, StoredSession } from '../types';
 
 export async function getProfileAlias(): Promise<string> {
-  const { profileAlias } = await chrome.storage.local.get<{ profileAlias?: string }>("profileAlias");
+  const { profileAlias } = await api.storage.local.get<{ profileAlias?: string }>("profileAlias");
   return profileAlias || "default";
 }
 
@@ -20,11 +21,11 @@ export function getSessionTabs(session: StoredSession | undefined | null): Sessi
 }
 
 export async function getAliases(): Promise<Record<string, string>> {
-  const { windowAliases } = await chrome.storage.local.get<{ windowAliases?: Record<string, string> }>("windowAliases");
+  const { windowAliases } = await api.storage.local.get<{ windowAliases?: Record<string, string> }>("windowAliases");
   return windowAliases || {};
 }
 
 export async function getSessions(): Promise<Record<string, StoredSession>> {
-  const { sessions } = await chrome.storage.local.get<{ sessions?: Record<string, StoredSession> }>("sessions");
+  const { sessions } = await api.storage.local.get<{ sessions?: Record<string, StoredSession> }>("sessions");
   return sessions || {};
 }