fix: address code review findings for OpenCode integration

- Add _isStopped guard to OpenCode 3s readiness timeout (session.ts)
- Block respawn for opencode sessions on interactive-respawn and
  respawn/enable routes (server.ts)
- Fail fast in direct PTY fallback for OpenCode mode (session.ts)
- Validate configContent as JSON at schema level (schemas.ts)
- Update JSDoc example for createSession options API (tmux-manager.ts)
- Un-hide Context tab for OpenCode sessions (index.html)
- Add OpenCode UI tests (opencode-resize.test.ts)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/session.ts

@@ -989,6 +989,7 @@ export class Session extends EventEmitter {
             // Emit needsRefresh so the client fetches the full buffer once the TUI has rendered.
             this._promptCheckTimeout = setTimeout(() => {
               this._promptCheckTimeout = null;
+              if (this._isStopped) return;
               this._status = 'idle';
               this.emit('needsRefresh');
             }, 3000);
@@ -1035,6 +1036,10 @@ export class Session extends EventEmitter {
 
     // Fallback to direct PTY if mux is not used
     if (!this.ptyProcess) {
+      // OpenCode sessions require tmux for env var injection (API keys via setenv)
+      if (this.mode === 'opencode') {
+        throw new Error('OpenCode sessions require tmux. Direct PTY fallback is not supported.');
+      }
       try {
         // Pass --session-id to use the SAME ID as the Claudeman session
         // This ensures subagents can be directly matched to the correct tab