fix(setup,ui): risolve errori setup + logo SVG theme-aware

- setup: corregge path templates (sibling di api/, non figlio) e firma TemplateResponse
- setup: invalida sessione client dopo operazioni che ruotano l'API key (init DB, creazione admin, cambio password, attivazione utente)
- api_client: include il nome del campo nei messaggi di errore 422 (FastAPI validation)
- ui: nuovo componente _app_logo.html (SVG inline theme-aware) usato su login e navbar

src/frontend/flask_app/services/api_client.py

@@ -56,11 +56,21 @@ class APIClient:
         try:
             error_body = response.json()
             detail = error_body.get("detail", str(error_body))
-            # FastAPI 422 returns detail as a list of validation errors
+            # FastAPI 422 returns detail as a list of validation errors:
+            # [{"type": ..., "loc": ["body", "password"], "msg": "...", ...}, ...]
             if isinstance(detail, list):
-                detail = "; ".join(
-                    e.get("msg", str(e)) for e in detail if isinstance(e, dict)
-                ) or str(detail)
+                parts = []
+                for e in detail:
+                    if not isinstance(e, dict):
+                        parts.append(str(e))
+                        continue
+                    msg = e.get("msg", str(e))
+                    loc = e.get("loc") or []
+                    # Strip leading "body"/"query"/"path" segments; keep field path.
+                    field_path = [str(p) for p in loc if p not in ("body", "query", "path")]
+                    field = ".".join(field_path) if field_path else None
+                    parts.append(f"{field}: {msg}" if field else msg)
+                detail = "; ".join(parts) or str(detail)
         except Exception:
             detail = response.text or f"HTTP {response.status_code}"