Fix over-correlation: geocoding precision, thin path ambiguity, skip_reason propagation

- Geocoding: reject GEOMETRIC_CENTER/APPROXIMATE results — vague location strings
  (regions, city centroids) were resolving to node-area coords and creating false
  proximity matches that merged unrelated incidents
- Thin path: on dispatch channels with multiple active incidents, skip attachment
  rather than guessing — "10-4" with 3 active incidents is genuinely ambiguous
- Short transcripts (≤5 words) now write skip_reason="transcript_too_short" to
  the call doc, matching garbage transcript behavior
- upload.py no-scenes fallback now checks skip_reason before running correlation —
  flagged calls (garbage, too short) no longer attach via thin path
- Update Server README to reflect current project purpose, goals, and pipeline

drb-c2-core/app/internal/intelligence.py

@@ -171,6 +171,10 @@ async def extract_scenes(
             f"Intelligence: call {call_id} — transcript too short for extraction "
             f"({len(transcript.split())} words), skipping"
         )
+        try:
+            await fstore.doc_set("calls", call_id, {"skip_reason": "transcript_too_short"})
+        except Exception:
+            pass
         return []
 
     raw_scenes: list[dict] = await asyncio.to_thread(
@@ -382,7 +386,19 @@ async def _geocode_location(
             data = r.json()
             if data.get("status") != "OK" or not data.get("results"):
                 return None
-            loc = data["results"][0]["geometry"]["location"]
+            result = data["results"][0]
+            location_type = result.get("geometry", {}).get("location_type", "")
+            # Only accept address-level precision. GEOMETRIC_CENTER (city/neighborhood
+            # centroid) and APPROXIMATE (region boundary) produce coordinates that look
+            # valid but are too vague for 0.5km proximity matching — they often resolve
+            # to the same point as the node's position and create false proximity matches.
+            if location_type not in ("ROOFTOP", "RANGE_INTERPOLATED"):
+                logger.info(
+                    f"Geocoding rejected '{location_str}' — imprecise result "
+                    f"(location_type={location_type!r}), returning None"
+                )
+                return None
+            loc = result["geometry"]["location"]
             lat, lng = float(loc["lat"]), float(loc["lng"])
             dist_km = _geo_dist_km(node_lat, node_lon, lat, lng)
             if dist_km > settings.geocode_max_km:
@@ -392,7 +408,7 @@ async def _geocode_location(
                 )
                 return None
             coords = {"lat": lat, "lng": lng}
-            logger.info(f"Geocoded '{location_str}' → {coords} ({dist_km:.1f}km from node)")
+            logger.info(f"Geocoded '{location_str}' → {coords} ({dist_km:.1f}km from node) [{location_type}]")
             return coords
     except Exception as e:
         logger.warning(f"Geocoding failed for '{location_str}': {e}")