Previous fix in 9dbf1ec6 handled Ctrl+C inside textInput but the APP-level
useInputHandlers fires the same keypress in a separate React hook and ran
clearIn() regardless. Net effect: the OSC 52 copy succeeded but the input
wiped right after, so Brooklyn only noticed the wipe.
Lift the selection-aware Ctrl+C to a single place by threading input
selection state through a new nanostore (src/app/inputSelectionStore.ts).
textInput syncs its derived `selected` range + a clear() callback to the
store on every selection change, and the app-level Ctrl+C handler reads
the store before its clear/interrupt/die chain:
- terminal-level selection (scrollback) → copy, existing behavior
- in-input selection present → copy + clear selection, preserve input
- input has text, no selection → clearIn(), existing behavior
- empty + busy → interrupt turn
- empty + idle → die
textInput no longer has its own Ctrl+C block; keypress falls through to
app-level like it did before 9dbf1ec6.
