Initial commit: webmail client (M0/M1)

Three-pane webmail client.
- Backend: FastAPI + async SQLAlchemy + arq worker (Postgres/Redis), IMAP/SMTP
  sync, threading, search, drafts/outbox with undo, attachments, 2FA.
- Frontend: React 18 + Vite + TypeScript + TanStack Query + Tailwind; three-pane
  UI with rich-text composer, light/dark themes, resizable panels.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/useKeyboardShortcuts.ts

@@ -0,0 +1,83 @@
+import { useEffect, useRef } from "react";
+
+// Keyboard shortcuts (SPEC §9.4). Ignores keystrokes while typing in inputs,
+// except Escape. Supports the `g i` chord (go to inbox).
+export interface Shortcuts {
+  onSearch?: () => void;
+  onCompose?: () => void;
+  onReply?: () => void;
+  onReplyAll?: () => void;
+  onForward?: () => void;
+  onArchive?: () => void;
+  onGoInbox?: () => void;
+  onEscape?: () => void;
+  onNext?: () => void;
+  onPrev?: () => void;
+}
+
+function isTyping(el: EventTarget | null): boolean {
+  if (!(el instanceof HTMLElement)) return false;
+  const tag = el.tagName;
+  return tag === "INPUT" || tag === "TEXTAREA" || el.isContentEditable;
+}
+
+export function useKeyboardShortcuts(shortcuts: Shortcuts): void {
+  const ref = useRef(shortcuts);
+  ref.current = shortcuts;
+  const pendingG = useRef(false);
+
+  useEffect(() => {
+    const handler = (e: KeyboardEvent) => {
+      const s = ref.current;
+      if (e.key === "Escape") {
+        s.onEscape?.();
+        return;
+      }
+      if (isTyping(e.target)) return;
+      if (e.metaKey || e.ctrlKey || e.altKey) return;
+
+      if (pendingG.current) {
+        pendingG.current = false;
+        if (e.key === "i") {
+          e.preventDefault();
+          s.onGoInbox?.();
+          return;
+        }
+      }
+
+      switch (e.key) {
+        case "/":
+          e.preventDefault();
+          s.onSearch?.();
+          break;
+        case "c":
+          s.onCompose?.();
+          break;
+        case "r":
+          s.onReply?.();
+          break;
+        case "a":
+          s.onReplyAll?.();
+          break;
+        case "f":
+          s.onForward?.();
+          break;
+        case "e":
+          s.onArchive?.();
+          break;
+        case "j":
+          s.onNext?.();
+          break;
+        case "k":
+          s.onPrev?.();
+          break;
+        case "g":
+          pendingG.current = true;
+          window.setTimeout(() => (pendingG.current = false), 800);
+          break;
+      }
+    };
+    window.addEventListener("keydown", handler);
+    return () => window.removeEventListener("keydown", handler);
+  }, []);
+}