feat(ledger): derive readout ranks body-identical groups first; CSS fingerprints are declarations, not selectors (#2872, milestone 294)

The 2026-08 audit consolidated identical bodies under different names and
files (five auth views' CSS, two Workspace formatDate()s, four modal blocks)
while the derive readout led with name groups (to_dict ×25, main ×5, load ×6)
that were convention or coincidence.

- proposal_summary ranks dup:<sha> groups above name groups, wider file spread
  first, and carries `files`; scoped rows (#2869) are in the readout, since
  that is where view-level copies live.
- extract_definitions fingerprints a CSS rule by its declarations — the row
  identity already carries the selector — so .closed-msg / .error-block /
  .success-msg with one body are one dup group. One-time effect: judged css
  rows whose stored fingerprint predates this may show a recheck on the next
  refresh (the judgment stands; re-confirm).

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

src/scribe/services/coverage.py

@@ -185,8 +185,15 @@ def extract_definitions(text: str) -> list[Definition]:
                 end = j
                 break
         block = lines[i:end]
+        # A CSS rule's fingerprint is its DECLARATIONS, not its selector
+        # (#2872): the row's identity already carries the selector, and the
+        # question the fingerprint answers for derive grouping is "is this the
+        # same rule under another name?" — .closed-msg / .error-block /
+        # .success-msg with identical bodies are one dup group, not three
+        # lonely rows. Sym blocks keep their signature line in the hash.
+        hashed = block[1:] if kind == "css" and len(block) > 1 else block
         out.append(Definition(
-            kind, name, lines[i].strip()[:_SIGNATURE_CAP], _block_sha(block),
+            kind, name, lines[i].strip()[:_SIGNATURE_CAP], _block_sha(hashed),
             "\n".join(block), i,
         ))
     return out