fix(tui): use esc back to leave the session dashboard

[mkonopelski-gd]

What

On the session detail (dashboard) screen, returning to the sessions list required pressing b. Every other screen uses esc to go back. This aligns the dashboard with the app-wide convention: the binding is esc and it's labeled back — the same generic gesture users learn everywhere else (e.g. WorkspaceMessagesScreen), not a screen-specific key or a destination-specific label ("sessions").

Change

Two small edits in mcp_server/tui/app.py:

-        Binding("b", "sessions", "sessions"),
+        Binding("escape", "back", "back"),

-    def action_sessions(self) -> None:
+    def action_back(self) -> None:
         self.app.push_screen(SessionsScreen())

The footer now reads esc back (auto-generated from the binding), consistent with the rest of the TUI.

Why push, not pop

action_back keeps push_screen(SessionsScreen()) rather than pop_screen(), because the dashboard can be the root screen when the TUI is launched to resume an existing run (app.py:2116) — popping there would land on a blank screen. Pushing a fresh SessionsScreen also reloads session statuses.

Scope

Deliberately minimal. WorkspaceMessagesScreen already binds both esc and b; its redundant b alias is left alone since esc already works there.

Testing

uv run pytest tests/test_tui_app.py → 112 passed. No test asserted the old b binding or the action_sessions name (the check_action tests reference action names, not keys).