feat(tui): unify keyboard and mouse navigation

Declare every dashboard key as a Binding on the widget that owns it, and
generate the footer, activity tool chips and help screen from those
bindings so they cannot drift. The footer collapses to "? help · q quit"
under 80x24.

Add Home/End and PgUp/PgDn (one week) navigation, mouse-wheel selection on
the graphs, click-to-focus on every panel, and clickable footer chips.
Tab and Shift+Tab now visit only the dashboard panels.

tests/test_live_graph.py

@@ -281,7 +281,7 @@ class TestLiveActivityGraph:
             await pilot.pause()
             header = str(graph.query_one("#live-header").render())
             assert "1 intervals" in header
-            assert "w W/R" in str(app.query_one("#activity-tools").render())
+            assert "w Toggle read/write" in str(app.query_one("#activity-tools").render())
 
 
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