feat(ledger): the consumer map surfaces — every css row carries used_by on list_shapes, flag="unused-css" (the map's negative space, surfaced never deleted), derive groups and the write-path family carry consumers, the derive line says "used by N template(s)", coverage payload unused_css + the standing block; docs, SKILL, plugin 0.1.44; the two step-2 tests expected 5 edges where fan-out makes 6 (milestone 302 step 3, #2936)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scribe/services/plugin_context.py

@@ -1073,6 +1073,18 @@ def _derive_line(path: str, derive: list[dict]) -> str:
             # files. CSS is only ever grouped this way (note 2917) — a class
             # is a recipe, and the recipe is what gets derived or dismissed.
             what = f"is a repeated name with no canon — defined in {n} other file(s)"
+        # What renders a css family (milestone 302): the consumer count is
+        # the datum that separates a shared recipe from a scoped convention.
+        cons = f.get("consumers")
+        if cons is not None:
+            n_t = cons.get("count", 0)
+            used = f"; used by {n_t} template{'s' if n_t != 1 else ''}"
+            if cons.get("paths"):
+                used += ": " + ", ".join(f"`{x}`" for x in cons["paths"])
+                extra = n_t - len(cons["paths"])
+                if extra > 0:
+                    used += f" +{extra} more"
+            files += used
         # The dismissal reason the family most likely earns: a class name
         # reused for different purposes is scoped styling; a code name reused
         # across modules is convention plumbing.