Phase 3: Polish & PWA

Backend:
- DB: reactions table, invites table, reply_to column on messages
- gateway/events.go: added REACTION_ADD, REACTION_REMOVE events
- internal/reaction/handlers.go: reaction CRUD with WebSocket broadcast
- internal/invite/handlers.go: invite creation, info, join with code
- gateway/hub.go: presence tracking with idle detection
- gateway/client.go: idle timeout support

Frontend - Social:
- TypingIndicator: real-time 'user is typing...' display
- ReactionBar: emoji reactions on messages with counts
- EmojiPicker: searchable emoji grid for reactions
- ReplyBar: quoted reply display above messages
- MentionPopup: @mention autocomplete with user list

Frontend - PWA:
- manifest.json: PWA manifest with theme color and icons
- sw.js: service worker with cache-first strategy and push support
- stores/push.ts: push notification subscription management
- InstallPrompt: 'Add to Home Screen' banner

Frontend - Mobile:
- MobileNav: bottom nav bar for mobile (servers/channels/chat/members)
- MobileDrawer: slide-out drawer with server bar + channel list
- index.html: PWA meta tags, safe area viewport

Frontend - Polish:
- ThemeToggle: dark/light mode switch with localStorage persistence
- InviteModal: generate invite links with expiry and max uses
- JoinServer: /invite/:code join flow
- stores/typing.ts: typing indicator state management
- stores/presence.ts: real-time presence tracking
- tailwind.config.js: darkMode: 'class', light mode color tokens
- styles/index.css: light mode CSS variable overrides

web/src/components/ThemeToggle.tsx

@@ -0,0 +1,36 @@
+import { useState, useEffect } from 'react';
+
+type Theme = 'dark' | 'light';
+
+export function ThemeToggle() {
+  const [theme, setTheme] = useState<Theme>(() => {
+    const stored = localStorage.getItem('dumpster-theme');
+    return (stored === 'light' ? 'light' : 'dark');
+  });
+
+  useEffect(() => {
+    const root = document.documentElement;
+    if (theme === 'light') {
+      root.classList.add('light');
+      root.classList.remove('dark');
+    } else {
+      root.classList.add('dark');
+      root.classList.remove('light');
+    }
+    localStorage.setItem('dumpster-theme', theme);
+  }, [theme]);
+
+  const toggle = () => {
+    setTheme(prev => prev === 'dark' ? 'light' : 'dark');
+  };
+
+  return (
+    <button
+      onClick={toggle}
+      className="px-2 py-1 text-xs font-mono text-gb-fg-f hover:text-gb-orange transition-colors"
+      title={`Switch to ${theme === 'dark' ? 'light' : 'dark'} mode`}
+    >
+      [{theme === 'dark' ? 'light' : 'dark'}]
+    </button>
+  );
+}