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>

src/fabledassistant/services/email.py

@@ -0,0 +1,109 @@
+"""Email service for sending notifications via SMTP."""
+
+import logging
+from email.message import EmailMessage
+
+import aiosmtplib
+from sqlalchemy import select
+
+from fabledassistant.config import Config
+from fabledassistant.models import async_session
+from fabledassistant.models.setting import Setting
+from fabledassistant.models.user import User
+
+logger = logging.getLogger(__name__)
+
+SMTP_SETTING_KEYS = [
+    "smtp_host",
+    "smtp_port",
+    "smtp_username",
+    "smtp_password",
+    "smtp_from_address",
+    "smtp_from_name",
+    "smtp_use_tls",
+]
+
+
+async def get_smtp_config() -> dict[str, str]:
+    """Get SMTP config from admin's settings, falling back to env vars."""
+    config: dict[str, str] = {
+        "smtp_host": Config.SMTP_HOST,
+        "smtp_port": str(Config.SMTP_PORT),
+        "smtp_username": Config.SMTP_USERNAME,
+        "smtp_password": Config.SMTP_PASSWORD,
+        "smtp_from_address": Config.SMTP_FROM_ADDRESS,
+        "smtp_from_name": Config.SMTP_FROM_NAME,
+        "smtp_use_tls": "true" if Config.SMTP_USE_TLS else "false",
+    }
+
+    # Override with DB settings from admin user
+    async with async_session() as session:
+        result = await session.execute(
+            select(Setting)
+            .join(User, Setting.user_id == User.id)
+            .where(User.role == "admin", Setting.key.in_(SMTP_SETTING_KEYS))
+        )
+        for setting in result.scalars().all():
+            config[setting.key] = setting.value
+
+    return config
+
+
+async def is_smtp_configured() -> bool:
+    """Check if SMTP is configured (has a host set)."""
+    config = await get_smtp_config()
+    return bool(config.get("smtp_host"))
+
+
+async def send_email(to: str, subject: str, html_body: str) -> None:
+    """Send an email via SMTP."""
+    config = await get_smtp_config()
+    host = config.get("smtp_host")
+    if not host:
+        logger.debug("SMTP not configured, skipping email to %s", to)
+        return
+
+    port = int(config.get("smtp_port", "587"))
+    username = config.get("smtp_username", "")
+    password = config.get("smtp_password", "")
+    from_address = config.get("smtp_from_address", "")
+    from_name = config.get("smtp_from_name", "Fabled Assistant")
+    use_tls = config.get("smtp_use_tls", "true") == "true"
+
+    msg = EmailMessage()
+    msg["Subject"] = subject
+    msg["From"] = f"{from_name} <{from_address}>" if from_name else from_address
+    msg["To"] = to
+    msg.set_content(subject)  # plain text fallback
+    msg.add_alternative(html_body, subtype="html")
+
+    try:
+        await aiosmtplib.send(
+            msg,
+            hostname=host,
+            port=port,
+            username=username or None,
+            password=password or None,
+            start_tls=use_tls and port != 465,
+            use_tls=port == 465,
+        )
+        logger.info("Email sent to %s: %s", to, subject)
+    except Exception:
+        logger.exception("Failed to send email to %s: %s", to, subject)
+        raise
+
+
+async def send_test_email(to: str) -> None:
+    """Send a branded test email."""
+    html = """
+    <div style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; max-width: 480px; margin: 0 auto; padding: 24px;">
+        <div style="background: #6366f1; color: #fff; padding: 16px 24px; border-radius: 8px 8px 0 0; text-align: center;">
+            <h1 style="margin: 0; font-size: 20px;">Fabled Assistant</h1>
+        </div>
+        <div style="background: #f9fafb; padding: 24px; border: 1px solid #e5e7eb; border-top: none; border-radius: 0 0 8px 8px;">
+            <p style="margin: 0 0 12px; color: #374151;">Your SMTP configuration is working correctly.</p>
+            <p style="margin: 0; color: #6b7280; font-size: 14px;">This is a test email sent from your Fabled Assistant instance.</p>
+        </div>
+    </div>
+    """
+    await send_email(to, "Fabled Assistant - Test Email", html)