fix(desktop): ignore IME composition keydowns in keybind combo resolution

Chinese/Japanese/Korean IMEs emit keydown events during composition that
carry preedit keystrokes and the commit keypress (Enter/Space/Shift for
candidate selection). Treating them as combos fires unrelated keybinds —
e.g. typing 你 with a CJK IME could dispatch session.new and silently
open a new session.

Guard comboFromEvent():
- Bail out entirely while composing (event.isComposing or key === 'Process')
- Ignore keydowns whose event.key is a bare modifier name but whose code
  is a regular key — legacy IMEs that synthesize keystrokes (Q9 2002 sends
  key="Control" with code="KeyW") would otherwise canonicalize into
  phantom combos like mod+w that close the active tab.

Tested with Q9 (九方) legacy IME on Windows.

apps/desktop/src/lib/keybinds/combo.ts

@@ -50,6 +50,9 @@ const MODIFIER_CODES = new Set([
   'ShiftRight'
 ])
 
+// Modifier names as reported by `event.key` on a bare modifier keydown.
+const MODIFIER_KEYS = new Set(['Alt', 'Control', 'Meta', 'Shift'])
+
 function baseKeyFromCode(code: string): string | null {
   if (code.startsWith('Key')) {
     return code.slice(3).toLowerCase()
@@ -101,10 +104,28 @@ function baseKeyFromEventKey(key: string, shiftKey: boolean): string | null {
 // Returns the canonical combo for a keydown, or null while only modifiers are
 // held (so capture mode keeps waiting for a real key).
 export function comboFromEvent(event: KeyboardEvent): string | null {
+  // IME composition (Chinese/Japanese/Korean input): the keydown events
+  // during composition carry preedit keystrokes and the commit keypress
+  // (Enter/Space/Shift for candidate selection). Treating them as combos
+  // fires unrelated keybinds — e.g. typing 你 with a Chinese IME sent a
+  // keydown that dispatched `session.new` and silently opened a new session.
+  // Bail out entirely while composing.
+  if (event.isComposing || event.key === 'Process') {
+    return null
+  }
+
   if (MODIFIER_CODES.has(event.code)) {
     return null
   }
 
+  // A keydown whose `key` is a modifier name but whose `code` is a regular
+  // key is not a real modifier chord — legacy IMEs that synthesize keystrokes
+  // (Q9 2002 sends key="Control" with code="KeyW") produce these, and they
+  // would canonicalize to phantom combos (Ctrl+W → close active tab). Ignore.
+  if (MODIFIER_KEYS.has(event.key)) {
+    return null
+  }
+
   const base = baseKeyFromEventKey(event.key, event.shiftKey) ?? baseKeyFromCode(event.code)
 
   if (!base) {