fix: count a core file only where it is packed

verify kept its own copy of the placement rule and missed the flat RomM folder, so the report still counted 543 unreachable files as packed. It now asks the builder's ExtraPlacement. The README fraction counted every held core file, including those a platform cannot place or that a same-named packed file hides. It now counts what the pack holds.

scripts/generate_readme.py

@@ -63,7 +63,11 @@ def compute_coverage(
     present = ok + untested
     pct = (present / total * 100) if total > 0 else 0
     undeclared = result.get("undeclared_files", [])
-    core_present = sum(1 for u in undeclared if u.get("in_repo"))
+    # Held is not packed: a file the platform has no folder for, or one below
+    # a folder it lists flat, stays out of the pack the fraction describes.
+    core_present = sum(
+        1 for u in undeclared if u.get("in_repo") and u.get("in_pack", True)
+    )
     core_missing = len(undeclared) - core_present
     # Files a profile marks unsourceable never reach the undeclared list, so
     # the gap they represent has to be counted back in.