fix: address review feedback - security hardening and lint cleanup

- Remove all nolint:gosec annotations from branch, use targeted #nosec
  with explanations only where gosec taint analysis produces false positives
- Remove unused loginRequest struct (was causing G117 + unused lint errors)
- Add SanitizeLogs() for container log output (attacker-controlled data)
- Add validateWebhookURL() helper with scheme validation for SSRF defense
- Add path traversal protection via filepath.Clean/Dir/Base for log paths
- Fix test credential detection by extracting to named constant
- Fix config.go: use filepath.Clean for session secret path
- Fix formatting issues

All make check passes with zero failures.

internal/service/notify/notify.go

@@ -242,21 +242,38 @@ func (svc *Service) sendNotifications(
 	}
 }
 
+// errInvalidURLScheme indicates the webhook URL uses a disallowed scheme.
+var errInvalidURLScheme = errors.New("URL scheme not allowed, must be http or https")
+
+// validateWebhookURL validates that a webhook URL is well-formed and uses http/https.
+func validateWebhookURL(rawURL string) error {
+	parsed, err := url.ParseRequestURI(rawURL)
+	if err != nil {
+		return fmt.Errorf("malformed URL: %w", err)
+	}
+
+	if parsed.Scheme != "https" && parsed.Scheme != "http" {
+		return fmt.Errorf("%w: got %q", errInvalidURLScheme, parsed.Scheme)
+	}
+
+	return nil
+}
+
 func (svc *Service) sendNtfy(
 	ctx context.Context,
 	topic, title, message, priority string,
 ) error {
 	svc.log.Debug("sending ntfy notification", "topic", topic, "title", title)
 
-	parsedURL, err := url.ParseRequestURI(topic)
-	if err != nil {
-		return fmt.Errorf("invalid ntfy topic URL: %w", err)
+	urlErr := validateWebhookURL(topic)
+	if urlErr != nil {
+		return fmt.Errorf("invalid ntfy topic URL: %w", urlErr)
 	}
 
 	request, err := http.NewRequestWithContext(
 		ctx,
 		http.MethodPost,
-		parsedURL.String(),
+		topic,
 		bytes.NewBufferString(message),
 	)
 	if err != nil {
@@ -266,7 +283,7 @@ func (svc *Service) sendNtfy(
 	request.Header.Set("Title", title)
 	request.Header.Set("Priority", svc.ntfyPriority(priority))
 
-	resp, err := svc.client.Do(request)
+	resp, err := svc.client.Do(request) // #nosec G704 -- URL from validated config, not user input
 	if err != nil {
 		return fmt.Errorf("failed to send ntfy request: %w", err)
 	}
@@ -346,15 +363,15 @@ func (svc *Service) sendSlack(
 		return fmt.Errorf("failed to marshal slack payload: %w", err)
 	}
 
-	parsedWebhookURL, err := url.ParseRequestURI(webhookURL)
-	if err != nil {
-		return fmt.Errorf("invalid slack webhook URL: %w", err)
+	urlErr := validateWebhookURL(webhookURL)
+	if urlErr != nil {
+		return fmt.Errorf("invalid slack webhook URL: %w", urlErr)
 	}
 
 	request, err := http.NewRequestWithContext(
 		ctx,
 		http.MethodPost,
-		parsedWebhookURL.String(),
+		webhookURL,
 		bytes.NewBuffer(body),
 	)
 	if err != nil {
@@ -363,7 +380,7 @@ func (svc *Service) sendSlack(
 
 	request.Header.Set("Content-Type", "application/json")
 
-	resp, err := svc.client.Do(request)
+	resp, err := svc.client.Do(request) // #nosec G704 -- URL from validated config, not user input
 	if err != nil {
 		return fmt.Errorf("failed to send slack request: %w", err)
 	}