feat: unread indicators + DM bug fixes + data-driven isDmChannel

- Fix stale message cache: add force param to loadMessages, clearAllMessages action
- Fix reload race condition: URL-based isDmChannel fallback before WS ready
- Add read_states DB table for persistent unread tracking
- Add channel_ack WS event (client→server→echo) with BigInt comparison
- Wire up unread state in chatStore (readStates, unreadChannels, ackChannel)
- Auto-ack channels on MessageList view (200ms debounced)
- Unread pill indicators on server icons in ServerSidebar
- Bold text + white dot on unread channels/DMs in ChannelSidebar
- Replace all showDms reads with data-driven isDmChannel() across 8 files
- Design system, UI polish, and component fixes from previous sessions

packages/web/src/components/auth/LoginPage.tsx

@@ -33,7 +33,7 @@ export function LoginPage() {
 
   return (
     <div className="min-h-screen flex items-center justify-center bg-discord-bg-tertiary">
-      <div className="w-full max-w-[480px] bg-discord-bg-primary rounded-md p-8 shadow-2xl">
+      <div className="w-full max-w-[480px] bg-discord-bg-surface rounded-md p-8 shadow-elevation-high">
         <div className="text-center mb-6">
           <h1 className="text-2xl font-bold text-discord-text-primary">Welcome back!</h1>
           <p className="text-discord-text-muted mt-1">We're so excited to see you again!</p>
@@ -41,7 +41,7 @@ export function LoginPage() {
 
         <form onSubmit={handleSubmit}>
           {error && (
-            <div className="mb-4 p-3 bg-discord-red/10 border border-discord-red/30 rounded text-discord-red text-sm">
+            <div className="mb-4 p-3 bg-discord-red/10 border border-discord-red/30 rounded text-discord-text-danger text-sm">
               {error}
             </div>
           )}
@@ -83,7 +83,7 @@ export function LoginPage() {
 
           <p className="mt-3 text-sm text-discord-text-muted">
             Need an account?{' '}
-            <Link to="/register" className="text-[#00aff4] hover:underline">
+            <Link to="/register" className="text-discord-text-link hover:underline">
               Register
             </Link>
           </p>