fix(geo): classify roof/shelter volumes so no block height is a guess

The three ways the height report flagged as guessed-height buildings are not
buildings: two are building=roof at layer=1 (elevated canopies) and one is an
amenity=shelter (public_transport). The report's '2 levels x 3.2 m' default
invented the 6.4 m figure. block_height_report.py now classifies them explicitly;
the block now reports 0 guessed heights, all 15 volumes having a real height tag,
a levels derivation, or a non-building classification.

Also records the measured hero proportions (colonnade 6.90 m = 47.6% of the
14.50 m envelope) for the open proportion task, which needs photo review.

Geo/tools/block_height_report.py

@@ -45,7 +45,14 @@ def main():
             continue
         tag_height = tags.get("height")
         levels = tags.get("building:levels")
-        if tag_height:
+        # Non-building volumes must not be extruded as two-storey blocks: a
+        # `building=roof` is an elevated slab and a public-transport shelter is a
+        # small street structure. Treating them as "2 levels x 3.2 m" produced a
+        # 6.4 m block for a bus shelter and a canopy.
+        if tags.get("building") == "roof" or tags.get("amenity") == "shelter":
+            kind = "roof" if tags.get("building") == "roof" else "shelter"
+            height, source = 0.0, f"not a building volume ({kind})"
+        elif tag_height:
             height, source = float(tag_height), "height tag"
         elif levels:
             height, source = float(levels) * LEVEL_HEIGHT, f"levels x {LEVEL_HEIGHT} m"
@@ -60,7 +67,8 @@ def main():
     guessed = [r for r in rows if r[5].startswith("GUESS")]
     print(f"{len(rows)} buildings in the block, {len(guessed)} with a guessed height\n")
     for side, setback, wid, name, height, source in rows:
-        flag = "  <-- guessed" if source.startswith("GUESS") else ""
+        flag = ("  <-- guessed" if source.startswith("GUESS")
+                else ("  <-- not a building volume" if source.startswith("not a building") else ""))
         print(f"{side} way {wid:>10}  setback {setback:5.1f} m  height {height:5.1f} m  "
               f"({source:26})  {name[:34]}{flag}")