fix: robust agent-to-tab connection lines with persistent parent tracking

- Add --session-id flag to Claude CLI startup so Claudeman and Claude share the same session ID
- Set claudeSessionId immediately on session start (no waiting for JSON messages)
- Add persistent subagentParentMap to store agent-to-tab associations permanently
- Add /api/subagent-parents endpoints for server-side persistence
- Add fallback: use active session when claudeSessionId matching fails
- Connection lines now reliably connect agent windows to their parent tabs
- Survives page refresh, reconnect, and server restart

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/screen-manager.ts

@@ -266,8 +266,10 @@ export class ScreenManager extends EventEmitter {
     ].join(' && ');
 
     // Base command for the mode (just the executable, env vars are exported separately)
+    // For Claude sessions: pass --session-id to use the SAME ID as the Claudeman session
+    // This ensures subagents (discovered via file path) can be directly matched to the correct tab
     const baseCmd = mode === 'claude'
-      ? 'claude --dangerously-skip-permissions'
+      ? `claude --dangerously-skip-permissions --session-id ${sessionId}`
       : '$SHELL';
 
     // Apply nice priority if configured