fix(typecheck): install tui optional dep in typecheck nox session

The typecheck session was installing only the base package (-e .)
without the tui optional dependency, so pyright could not resolve
the textual.geometry, textual.reactive, and textual.widgets imports
that prompt.py conditionally loads when _TEXTUAL_AVAILABLE is True.

Changing to -e .[tui] ensures textual is present in the typecheck
venv so pyright reports no reportMissingImports errors.

noxfile.py

@@ -162,7 +162,7 @@ def format(session: nox.Session):
 def typecheck(session: nox.Session):
     """Check types with pyright."""
     session.install("pyright")
-    session.install("-e", ".")
+    session.install("-e", ".[tui]")
     session.run("pyright", stderr=sys.stdout)