feat(cookie): Deklaration-vs-Bibliothek-Diff-Sicht + Funnel-KPI

Für die Library-getroffene Teilmesse (~32%) pro Cookie die Feld-
Abweichungen deklariert→Library (Kategorie/Laufzeit/Zweck) als Diff-Karte,
plus ehrlicher Funnel (gesamt → geprüft → abweichend) — nicht-getroffene
Cookies sind nicht prüfbar (kein Pass/Fail), passend zur Tonalität.

- analyze_cookies: 'expected'-Soll-Wert an tracker_as_necessary/
  excessive_lifetime/missing_purpose (+ _CAT_LABEL_DE).
- neues cookie_declaration_diff.build_declaration_diff: reine Regroup-
  Aggregation der Findings pro Cookie (single source = analyze_cookies),
  Hinweis-Typen (third_country/eu_alternative) bewusst ausgeschlossen.
- cookie-check exponiert out['declaration_diff'].
- CookieDeclarationDiff.tsx oben im Cookie-Tab (vor Panel/ResultView).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend-compliance/compliance/api/snapshot_check_routes.py

@@ -80,6 +80,11 @@ async def snapshot_cookie_check(snapshot_id: str):
             out["findings"].insert(0, tf)
             out["summary"]["findings"] = len(out["findings"])
         out["storage_inventory"] = inv
+        # Deklaration-vs-Bibliothek-Diff (nur die getroffene Teilmenge) + Funnel.
+        from compliance.services.cookie_declaration_diff import (
+            build_declaration_diff,
+        )
+        out["declaration_diff"] = build_declaration_diff(out)
         # ② Documentation Drift: Cookie-Richtlinie (Text) vs. Browser-Realität.
         docs = snap.get("doc_entries") or []
         cookie_text = next(