feat(shapes): the write-path hook suggests and no longer stamps (milestone 439 step 4)

The hook used to land its evidence as `instance` rows, classified_by=hook —
a permanent verdict nobody read, and the source of the weak stamps that
poisoned two ledgers (#4608). Now the agent that wrote the code judges it at
the end of the turn, and the hook's evidence is what it is shown.

- shape_ledger.suggest_write_path_instances (was stamp_write_path_instances):
  same evidence and form gate, but it writes a PROPOSAL — proposed_snippet_id,
  basis "reference" (named) or "semantic" (resembles), score — and never a
  status. A judged row is left alone; a new shape gets an unclassified
  provisional row so the suggestion reaches the end-of-turn question as
  "looks like #N". By-name uses edges stay: a fact, not a verdict.
- The prior-art line says "looks like #N … when you judge this turn's
  shapes, say whether it is", and the result key is `suggested`.
- write_time_divergence takes `suggested`; _RESEMBLE_MIN re-documented as the
  suggestion bar and the weak-stamp line.
- reusing-code skill no longer says the pull stamps an instance.
- Tests moved to the new contract, plus a guard that nothing the hook does
  writes classified_by="hook".

Plugin version minted.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugin/skills/reusing-code/SKILL.md

@@ -34,9 +34,9 @@ through recall/auto-inject; this skill is the active reflex around that.
   to ask both at once.
 - If a snippet fits, pull it in full with `get_snippet(id)` and reuse it — its
   `location` points at the reference implementation. Adapt, don't re-derive.
-  The pull also does the accounting: the code you then write that references
-  or resembles it is stamped an `instance` of that canon in the shape ledger
-  (classified_by=hook) — reuse from memory leaves no row.
+  The pull also feeds the accounting: the code you then write that references
+  or resembles it is offered back to you as "looks like #N" when you judge the
+  turn's shapes — reuse from memory leaves no such evidence.
 - If auto-inject already surfaced a snippet title that looks relevant, that's
   your cue to `get_snippet` it rather than start from scratch.
 - **Prior art offered beside a write is not noise — read it.** When Scribe notes