feat: comprehensive debug logging across all controller modules

Add detailed [DEBUG] logging to every controller module when
logging.level is set to "debug". Each module with stateful debug
uses SetDebug(bool) wired from main.go. Covers stacks, backup,
cloudflare, integrations, system, monitor, settings, scheduler,
web handlers, storage, metrics, API, selfupdate, and assets.

Also includes the app export/import (.fab bundles) feature from
v0.32.0 and its debug page integration.

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

controller/internal/cloudflare/zone.go

@@ -16,7 +16,14 @@ type zone struct {
 // GetZoneID resolves the Cloudflare zone ID for a domain.
 // It tries the exact domain first, then strips subdomains progressively.
 func (c *Client) GetZoneID(ctx context.Context, domain string) (string, error) {
+	if c.debug {
+		c.logger.Printf("[CF-DEBUG] GetZoneID: looking up zone for domain %q", domain)
+	}
+
 	// Try exact domain first (e.g., "demo-felhom.eu")
+	if c.debug {
+		c.logger.Printf("[CF-DEBUG] GetZoneID: trying exact domain %q", domain)
+	}
 	id, err := c.lookupZone(ctx, domain)
 	if err != nil {
 		return "", err
@@ -32,6 +39,9 @@ func (c *Client) GetZoneID(ctx context.Context, domain string) (string, error) {
 			if parent == "" {
 				break
 			}
+			if c.debug {
+				c.logger.Printf("[CF-DEBUG] GetZoneID: trying parent domain %q", parent)
+			}
 			id, err = c.lookupZone(ctx, parent)
 			if err != nil {
 				return "", err