fix(terminal): macOS Vietnamese Telex keeps its capitals in Chrome too

macOS's own Vietnamese Telex types into xterm's textarea with no
composition events: a letter is an `insertText`, every later key of the
word an `insertReplacementText`, each keydown (keyCode 229) arriving after
the change. v2.7.4 forwarded the replacements, but a capital typed with
Shift still vanished — xterm drops any `input` that lands while a key is
held — and its 229 fallback could resend an edit. Replayed from a real
Chrome trace, "Abc xin chào" reached the pane as " x c".

lib/imeInput.ts now owns those edits: capture phase on xterm's element,
each one sent as DELs plus the new tail, the IME's input and 229 keydowns
hidden from xterm. Keys xterm sends from keypress (Space) and real
compositions (CJK) stay xterm's. Verified against xterm 5.5 in headless
Chrome: Telex → "Abc xin chào"; a plain keyboard sends the same bytes
as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

client/src/components/run/__tests__/TerminalView.test.tsx

@@ -75,6 +75,8 @@ vi.mock("@xterm/xterm", () => ({
     paste: pasteMock,
     input: inputMock,
     textarea: (textarea = document.createElement("textarea")),
+    // xterm's own element, holding its textarea (lib/imeInput listens on it).
+    element: document.createElement("div").appendChild(textarea).parentElement,
     resize: (cols: number, rows: number) => Object.assign(termState, { cols, rows }),
   })),
 }));