Fix subagent crash and add external OpenCode server support (#188)

* 🐛 Fix UI crash when subagent is active

Remove sessions dependency from hooks to prevent cascading re-renders.
Use getState() instead and switch to getGlobalSessionStatus().

* ✨ Add support for connecting to external OpenCode server

Add OPENCODE_SKIP_START env var to skip starting embedded server.
Use OPENCODE_PORT to connect to existing OpenCode instance.
Update help text to document the new environment variables.

* 📝 Document external OpenCode server support

Add OPENCODE_PORT and OPENCODE_SKIP_START to READMEs.
Update AGENTS.md with external server integration notes.

* ✨ Add URL-based routing for shareable session links

- Add react-router-dom dependency
- Create URL store for bi-directional sync with Zustand
- Add WebRouter/DesktopRouter context for runtime-aware routing
- Add useURLSync hook to sync URL with session/tab state
- Add useNavigation hook with copySessionLink utility
- Add share button in Header for copying session links
- Update App.tsx to use router wrappers

URL structure:
  /session/:sessionId?tab={chat|git|diff|terminal|files}&directory=/path
  /settings

This enables shareable links and deep-linking to specific sessions.

* Revert "✨ Add URL-based routing for shareable session links"

This reverts commit b53ee304950a789538fa3d4a236d6361e634ea61.

packages/ui/src/hooks/useSessionStatusBootstrap.ts

@@ -15,7 +15,9 @@ export const useSessionStatusBootstrap = () => {
 
     const bootstrap = async () => {
       try {
-        const statusMap = await opencodeClient.getSessionStatus();
+        // Use global status to detect busy sessions across all directories,
+        // including sessions started externally (e.g., via CLI) before UI opened
+        const statusMap = await opencodeClient.getGlobalSessionStatus();
         if (cancelled || !statusMap) return;
 
         const phases = new Map<string, 'idle' | 'busy' | 'cooldown'>();