fix(keymap): match remaining letter shortcuts by typed character (#292)

#291 named letter keys by the typed character (e.key) when Alt is not held, so AZERTY Ctrl+Z is no longer Ctrl+W. Hard-coded handlers still compared the physical KeyboardEvent.code. A shared letterOf(e) in platform/keymap.ts now backs strokeOf and those handlers:

- terminal Ctrl+Shift+C / V / T (copy, paste, new tab) and Ctrl+letter control codes
- Run/Debug Configurations Ctrl/Cmd+N
- browser shortcut guards (blocked reload/print etc.)

Alt combos keep the physical key (Option / AltGr type symbols).

src/platform/keymap.test.ts

@@ -4,6 +4,7 @@ import {
   installKeyboardDispatcher,
   isAltGrTyping,
   isValidBinding,
+  letterOf,
   normalizeBinding,
   parseDoubleModifier,
   strokeOf,
@@ -31,6 +32,9 @@ describe("keymap", () => {
 
   it("names letters by the character typed, so AZERTY's Ctrl+Z is not Ctrl+W", () => {
     // AZERTY: the key typing "z" is physically KeyW.
+    expect(letterOf({ code: "KeyW", key: "z", altKey: false })).toBe("Z");
+    expect(letterOf({ code: "KeyF", key: "ƒ", altKey: true })).toBe("F");
+    expect(letterOf({ code: "Digit1", key: "1", altKey: false })).toBeNull();
     expect(strokeOf({ code: "KeyW", key: "z", metaKey: false, ctrlKey: true, altKey: false, shiftKey: false })).toBe(
       "Ctrl+Z",
     );