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/web/server/index.js

@@ -1340,6 +1340,9 @@ const ENV_CONFIGURED_OPENCODE_PORT = (() => {
   return Number.isFinite(parsed) && parsed > 0 ? parsed : null;
 })();
 
+const ENV_SKIP_OPENCODE_START = process.env.OPENCODE_SKIP_START === 'true' ||
+                                   process.env.OPENCHAMBER_SKIP_OPENCODE_START === 'true';
+
 const ENV_CONFIGURED_API_PREFIX = normalizeApiPrefix(
   process.env.OPENCODE_API_PREFIX || process.env.OPENCHAMBER_API_PREFIX || ''
 );
@@ -5664,12 +5667,17 @@ async function main(options = {}) {
 
 
   try {
-    // Check if we can reuse an existing OpenCode process from a previous HMR cycle
     syncFromHmrState();
     if (await isOpenCodeProcessHealthy()) {
       console.log(`[HMR] Reusing existing OpenCode process on port ${openCodePort}`);
+    } else if (ENV_SKIP_OPENCODE_START && ENV_CONFIGURED_OPENCODE_PORT) {
+      console.log(`Using external OpenCode server on port ${ENV_CONFIGURED_OPENCODE_PORT} (skip-start mode)`);
+      setOpenCodePort(ENV_CONFIGURED_OPENCODE_PORT);
+      isOpenCodeReady = true;
+      lastOpenCodeError = null;
+      openCodeNotReadySince = 0;
+      syncToHmrState();
     } else {
-      // No healthy process, start fresh
       if (ENV_CONFIGURED_OPENCODE_PORT) {
         console.log(`Using OpenCode port from environment: ${ENV_CONFIGURED_OPENCODE_PORT}`);
         setOpenCodePort(ENV_CONFIGURED_OPENCODE_PORT);