hub v0.42.0: remote "Debug mód" toggle on the customer config editor

Adds a form-level debug-mode checkbox to the customer config editor so an
operator can flip the controller's Logging.Level=debug (/debug menu + verbose
log) remotely, without SSH. Form field (not raw-JSON injection) because
handleConfigUpdate rebuilds ConfigJSON from the form on every save; the
config-version bump makes the controller re-pull + self-restart next cycle.

- buildConfigJSON: debug_mode checked -> "logging":{"level":"debug"};
  unchecked -> logging key omitted.
- config_form.html: "Hibakeresési mód (fejlesztői)" section + render state.
- configs_debug_test.go: form->JSON both ways; full-path survival test
  (debug lands, offsite descriptor unchanged, foreign-key red-proof); render
  state; red-proof exercised.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

hub/internal/web/templates/config_form.html

@@ -103,6 +103,18 @@
                 </div>
             </details>
 
+            <details class="card" {{if index .Overrides "logging"}}open{{end}}>
+                <summary><h2 style="display:inline">Hibakeresési mód (fejlesztői)</h2></summary>
+                <div class="form-grid" style="margin-top: 1rem;">
+                    <div class="form-group">
+                        <label><input type="checkbox" name="debug_mode"
+                            {{with .Overrides}}{{with index . "logging"}}{{if eq (index . "level") "debug"}}checked{{end}}{{end}}{{end}}>
+                            Debug mód — bőbeszédű napló + /debug menü a vezérlőn</label>
+                        <small class="form-hint">Bekapcsolva a vezérlő újraindul a következő ciklusban; a menü: https://felhom.&lt;domain&gt;/debug. Tesztelés után kapcsold ki.</small>
+                    </div>
+                </div>
+            </details>
+
             <details class="card" {{if index .Overrides "offsite"}}open{{end}}>
                 <summary><h2 style="display:inline">Offsite backup</h2></summary>
                 <div class="form-grid" style="margin-top: 1rem;">