feat(api): add setup_complete system setting and status handlers

Add 'setup_complete' boolean to the system_settings seed data (defaults
to false) so fresh databases start in the unconfigured state.

Add two new handlers to SystemSettingsHandler:
- SetSetupComplete: marks setup_complete=true in the database
- GetSetupStatus: reads the current setup_complete value, returns
  {setup_complete: bool} JSON response, defaults to false if the
  setting row is missing or unparseable

internal/handlers/system_settings.go

@@ -95,6 +95,32 @@ func (h *SystemSettingsHandler) UpdateScanSettings(c *echo.Context) error {
 	})
 }
 
+func (h *SystemSettingsHandler) SetSetupComplete(c *echo.Context) error {
+	err := h.db.UpdateSystemSetting(c.Request().Context(), database.UpdateSystemSettingParams{
+		SettingKey:   "setup_complete",
+		SettingValue: "true",
+	})
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+	}
+	return c.JSON(http.StatusOK, map[string]string{"message": "setup complete"})
+}
+
+func (h *SystemSettingsHandler) GetSetupStatus(c *echo.Context) error {
+	val, err := h.db.GetSystemSetting(c.Request().Context(), "setup_complete")
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return c.JSON(http.StatusOK, map[string]bool{"setup_complete": false})
+		}
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+	}
+	complete, err := strconv.ParseBool(val)
+	if err != nil {
+		complete = false
+	}
+	return c.JSON(http.StatusOK, map[string]bool{"setup_complete": complete})
+}
+
 func (h *SystemSettingsHandler) GetScanSettings(c *echo.Context) error {
 	scanFrequencySetting, err := h.db.GetSystemSetting(c.Request().Context(), "scan_poll_interval_seconds")
 	if err != nil {