fix(tui): add __future__ annotations — CI runner Python evaluates eagerly

The CI runner's Python (<3.14) evaluates type annotations eagerly, so
Static.Clicked in a method signature raises AttributeError at import.
Python 3.14 (local) has PEP 649 lazy annotations, which is why it works
locally. Adding from __future__ import annotations makes it lazy on all
versions.

src/rune/rune_tui.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+from __future__ import annotations
 """Rune TUI — the body.
 
 Textual-based terminal interface for Rune. Two channels (task + chat),