feat(FN-772): fix terminal startup and prompt delivery reliability

- Fix terminal service to ensure prompt is reliably delivered on startup and reconnect
- Add regression tests for terminal reconnect and first-paint behavior
- Remove dead code: unused global-settings tests, styles.css, Header/MissionManager tests
- Update terminal README with reliable prompt delivery guarantee documentation
- Add useTerminal hook tests and TerminalModal component tests

packages/dashboard/app/hooks/useTerminal.ts

@@ -99,6 +99,9 @@ export function useTerminal(sessionId: string | null): UseTerminalReturn {
     const buffer = initialBufferRef.current;
     if (buffer.data.length > 0) {
       buffer.data.forEach((d) => callback(d));
+      // Clear after replay to prevent stale re-delivery if a new subscriber
+      // registers later (e.g. due to a re-render or reconnect).
+      buffer.data = [];
     }
     return () => onDataCallbacksRef.current.delete(callback);
   }, []);
@@ -114,6 +117,8 @@ export function useTerminal(sessionId: string | null): UseTerminalReturn {
     const buffer = initialBufferRef.current;
     if (buffer.connected) {
       callback(buffer.connected);
+      // Clear after replay — connected info is one-shot
+      buffer.connected = null;
     }
     return () => onConnectCallbacksRef.current.delete(callback);
   }, []);
@@ -124,6 +129,8 @@ export function useTerminal(sessionId: string | null): UseTerminalReturn {
     const buffer = initialBufferRef.current;
     if (buffer.scrollback) {
       callback(buffer.scrollback);
+      // Clear after replay — scrollback is one-shot per connection
+      buffer.scrollback = null;
     }
     return () => onScrollbackCallbacksRef.current.delete(callback);
   }, []);