fix(impressum): sector-gate respects on-topic criteria (parity with DSE)

A clearly impressum-thematic control (e.g. MStV 18 with inherited GOV prefix) is no longer dropped by the sector-prefix gate - topic overlap is the stronger signal. Mirrors dse/v3_engine. Salvaged WIP.

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

backend-compliance/compliance/services/specialist_agents/impressum/v3_engine.py

@@ -182,12 +182,18 @@ def _filter_controls(
     for c in controls:
         cid = c.get("control_id") or ""
         prefix = cid.split("-")[0].upper() if "-" in cid else ""
+        on_topic = criteria_on_topic(c.get("pass_criteria"),
+                                     c.get("fail_criteria"))
         required = SECTOR_PREFIXES.get(prefix)
-        if required and not (scope_lc & required):
+        # Sektor-Gate nur fuer NICHT-on-topic Controls: ein klar
+        # impressum-thematischer Control (z.B. MStV §18(1) mit GOV-Prefix
+        # aus der Domain-Erkennung der Control-Generierung) darf nicht am
+        # Branchen-Prefix scheitern. Der Themen-Ueberlapp ist der staerkere
+        # Relevanz-Beweis als ein vererbter ID-Prefix.
+        if required and not (scope_lc & required) and not on_topic:
             sector_dropped += 1
             continue
-        if not criteria_on_topic(c.get("pass_criteria"),
-                                 c.get("fail_criteria")):
+        if not on_topic:
             offtopic_dropped += 1
             continue
         kept.append(c)