feat: Add direct messages (DM) support

- Parse PRIV (incoming) and SENT_MSG (outgoing) message types
- Add DM API endpoints: conversations, messages, updates
- Implement conversation grouping by pubkey_prefix or name
- Add timeout-based delivery status (pending → timeout)
- Add DM modal with conversation list and thread views
- Add dual notification badge (blue=channels, green=DM)
- Add DM button next to Reply on channel messages
- Include message deduplication for both incoming and outgoing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/static/css/style.css

@@ -329,3 +329,156 @@ main {
     transform: scale(1.1);
     transition: transform 0.2s ease;
 }
+
+/* =============================================================================
+   Direct Messages (DM) Styles
+   ============================================================================= */
+
+/* DM Badge on notification bell (secondary badge, bottom-right, green) */
+.notification-badge-dm {
+    position: absolute;
+    bottom: -6px;
+    right: -6px;
+    background-color: #198754;
+    color: white;
+    border-radius: 8px;
+    padding: 1px 4px;
+    font-size: 0.6rem;
+    font-weight: bold;
+    min-width: 14px;
+    text-align: center;
+    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
+    z-index: 10;
+}
+
+/* DM Messages Container */
+.dm-messages-container {
+    height: 50vh;
+    overflow-y: auto;
+    padding: 0.5rem;
+    display: flex;
+    flex-direction: column;
+    gap: 0.5rem;
+    background-color: #fafafa;
+}
+
+@media (max-width: 576px) {
+    .dm-messages-container {
+        height: calc(100vh - 200px);
+    }
+}
+
+/* DM Message Bubbles */
+.dm-message {
+    max-width: 80%;
+    padding: 0.5rem 0.75rem;
+    border-radius: 1rem;
+    font-size: 0.9rem;
+    word-wrap: break-word;
+    animation: fadeIn 0.2s ease-in;
+}
+
+.dm-message.own {
+    align-self: flex-end;
+    background-color: var(--msg-own-bg);
+    border: 1px solid #b8daff;
+}
+
+.dm-message.other {
+    align-self: flex-start;
+    background-color: var(--msg-other-bg);
+    border: 1px solid var(--msg-border);
+}
+
+/* DM Message Metadata */
+.dm-meta {
+    font-size: 0.65rem;
+    color: #adb5bd;
+    margin-top: 0.25rem;
+}
+
+/* DM Status Indicators */
+.dm-status {
+    font-size: 0.7rem;
+    margin-left: 0.25rem;
+}
+
+.dm-status.pending {
+    color: #ffc107;
+}
+
+.dm-status.delivered {
+    color: #198754;
+}
+
+.dm-status.timeout {
+    color: #dc3545;
+}
+
+/* DM Conversation List Item */
+.dm-conversation-item {
+    padding: 0.75rem;
+    border-bottom: 1px solid #dee2e6;
+    cursor: pointer;
+    transition: background-color 0.15s ease;
+}
+
+.dm-conversation-item:hover {
+    background-color: #f8f9fa;
+}
+
+.dm-conversation-item.unread {
+    background-color: #e7f1ff;
+}
+
+.dm-conversation-item:last-child {
+    border-bottom: none;
+}
+
+/* DM Preview Text */
+.dm-preview {
+    font-size: 0.85rem;
+    color: #6c757d;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    max-width: 100%;
+}
+
+/* DM Button on channel messages */
+.btn-dm {
+    font-size: 0.65rem;
+    padding: 0.1rem 0.3rem;
+    margin-left: 0.25rem;
+}
+
+/* DM Empty State */
+.dm-empty-state {
+    text-align: center;
+    padding: 2rem 1rem;
+    color: #6c757d;
+}
+
+.dm-empty-state i {
+    font-size: 2.5rem;
+    margin-bottom: 0.75rem;
+    opacity: 0.5;
+}
+
+/* DM Scrollbar */
+.dm-messages-container::-webkit-scrollbar {
+    width: 6px;
+}
+
+.dm-messages-container::-webkit-scrollbar-track {
+    background: #f1f1f1;
+}
+
+.dm-messages-container::-webkit-scrollbar-thumb {
+    background: #ccc;
+    border-radius: 3px;
+}
+
+.dm-messages-container::-webkit-scrollbar-thumb:hover {
+    background: #aaa;
+}