Add application logging, SMTP email notifications, and supporting changes

Phase 5.4 — Application Logging:
- AppLog model + migration 0010 for unified audit/usage/error logging
- Usage logging middleware in app.py (after_request for /api/* requests)
- Error logging in 500 handler with traceback capture
- Audit logging for auth events (register, login, login_failed, logout,
  password_change) and admin actions (backup, restore, user_delete,
  registration_toggle, smtp_config, smtp_test)
- Admin log viewer (LogsView.vue) with stats, category/search/date
  filters, paginated table with expandable detail rows
- Admin logs API endpoints in admin.py (GET /logs, GET /logs/stats)
- Configurable retention via LOG_RETENTION_DAYS with hourly cleanup

Phase 5.5 — SMTP Email Notifications:
- aiosmtplib dependency for async email sending
- Email service (services/email.py) with STARTTLS/implicit TLS support
- Notification service (services/notifications.py) for security alerts
  and task due date reminders with per-user preferences
- Admin SMTP config endpoints (GET/PUT /api/admin/smtp, POST test)
- SMTP config in Config class with env var + Docker secret support
- Settings UI: notification preferences for all users, SMTP config
  section for admin with test email

Other changes:
- stream_chat() now accepts optional options dict (for num_predict)
- Increase assist MAX_BODY_CHARS from 3000 to 8000
- get_user_by_username() added to auth service
- apiStreamPost buffer processing refactored for robustness
- AppHeader: admin Logs nav link
- Router: /admin/logs route

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/api/client.ts

@@ -226,22 +226,25 @@ export async function apiStreamPost(
   const decoder = new TextDecoder();
   let buffer = "";
 
-  function processLines(text: string) {
-    const lines = text.split("\n");
+  function processLine(line: string) {
+    const trimmed = line.trim();
+    if (trimmed.startsWith("data: ")) {
+      let data;
+      try {
+        data = JSON.parse(trimmed.slice(6));
+      } catch {
+        return; // Skip malformed JSON lines
+      }
+      onChunk(data);
+    }
+  }
+
+  function processBuffer() {
+    const lines = buffer.split("\n");
     // Keep the last (possibly incomplete) line in the buffer
     buffer = lines.pop() || "";
-
     for (const line of lines) {
-      const trimmed = line.trim();
-      if (trimmed.startsWith("data: ")) {
-        let data;
-        try {
-          data = JSON.parse(trimmed.slice(6));
-        } catch {
-          continue; // Skip malformed JSON lines
-        }
-        onChunk(data);
-      }
+      processLine(line);
     }
   }
 
@@ -250,22 +253,19 @@ export async function apiStreamPost(
       const { done, value } = await reader.read();
       if (done) break;
       buffer += decoder.decode(value, { stream: true });
-      processLines(buffer);
+      processBuffer();
     }
   } catch {
     // Stream may close with a network error after all data was sent.
-    // Process whatever remains in the buffer before deciding to throw.
   }
 
-  // Process any remaining buffer
-  const remaining = buffer.trim();
-  if (remaining.startsWith("data: ")) {
-    let data;
-    try {
-      data = JSON.parse(remaining.slice(6));
-    } catch {
-      return; // Skip malformed JSON
+  // Flush any remaining complete lines in the buffer
+  if (buffer.trim()) {
+    // The buffer may contain one or more unprocessed lines
+    const remaining = buffer;
+    buffer = "";
+    for (const line of remaining.split("\n")) {
+      processLine(line);
     }
-    onChunk(data);
   }
 }