feat: enrich correlation debug with fit_signal and orphan breakdown

_call_fits_incident now returns (bool, signal_str) so each correlation
decision records exactly what evidence fired: unit_overlap, vehicle_overlap,
location_proximity, time_fallback, tactical_default, or the corresponding
false-return variants (unit_loc_conflict, content_divergence, etc.).

- corr_fit_signal and corr_matched_units written to call docs for
  fast/single and fast/disambig paths
- Admin debug endpoint exposes the new fields in calls_detail
- Orphan section adds orphans_by_talkgroup summary (count, no-type count,
  sweep-exhausted count per TGID) and raises orphan limit 100 → 250
- Admin page shows corr_path and fit_signal distribution panels above raw
  JSON; time_fallback highlighted in yellow as a diagnostic marker

No correlation logic changed — diagnostic data only.

drb-c2-core/app/routers/admin.py

@@ -67,6 +67,8 @@ async def debug_correlation(
             "corr_score":            call.get("corr_score"),
             "corr_candidates":       call.get("corr_candidates"),
             "corr_shared_units":     call.get("corr_shared_units"),
+            "corr_fit_signal":       call.get("corr_fit_signal"),
+            "corr_matched_units":    call.get("corr_matched_units"),
             "corr_sweep_count":      call.get("corr_sweep_count"),
             "skip_reason":           call.get("skip_reason"),
         }
@@ -108,10 +110,29 @@ async def debug_correlation(
     ]
     orphans.sort(key=lambda c: c.get("started_at", ""), reverse=True)
 
+    # Summarise orphans by talkgroup so the volume and source are immediately visible.
+    orphans_by_tg: dict[str, dict] = {}
+    for o in orphans:
+        tg_key = str(o.get("talkgroup_id") or "unknown")
+        if tg_key not in orphans_by_tg:
+            orphans_by_tg[tg_key] = {
+                "talkgroup_id":   o.get("talkgroup_id"),
+                "talkgroup_name": o.get("talkgroup_name") or "unknown",
+                "count":          0,
+                "no_type_count":  0,
+                "sweep_exhausted_count": 0,
+            }
+        orphans_by_tg[tg_key]["count"] += 1
+        if not o.get("incident_type") and not o.get("tags"):
+            orphans_by_tg[tg_key]["no_type_count"] += 1
+        if (o.get("corr_sweep_count") or 0) >= 3:
+            orphans_by_tg[tg_key]["sweep_exhausted_count"] += 1
+
     return {
-        "generated_at":        datetime.now(timezone.utc).isoformat(),
-        "incident_count":      len(incident_records),
-        "orphaned_call_count": len(orphans),
-        "incidents":           incident_records,
-        "orphaned_calls":      orphans[:100],
+        "generated_at":           datetime.now(timezone.utc).isoformat(),
+        "incident_count":         len(incident_records),
+        "orphaned_call_count":    len(orphans),
+        "orphans_by_talkgroup":   sorted(orphans_by_tg.values(), key=lambda x: x["count"], reverse=True),
+        "incidents":              incident_records,
+        "orphaned_calls":         orphans[:250],
     }