fix(docs): the retirement guide's own notes examples do not load

Both "where the record goes" snippets in verified-by-retirement.md write `"notes"` BARE.
Canonical JSON reserves exactly eight structural keys (name/package/extends/abstract/
overlay/isArray/children/value); everything else is an inline attribute and must carry the
sigil. So the loader rejects it:

  Unknown key 'notes' on requirement.functional 'BeatProgression' — must be reserved or
  @-prefixed

Verified against a real strict load: bare `notes` errors, `@notes` loads and reads back.

This is the worst possible place for it. Those two snippets ARE the answer FR-038 gives to
the one objection adopters actually raise — "deleting the node destroys the history" — and
the answer is "put it in notes, here is how". An adopter who follows the example literally
gets a load failure while doing the migration the guide told them to do, which reads as the
retirement being half-baked rather than as a typo in a sample.

Found by testing the example rather than reading it, after being asked where notes had
gone. The two other bare-`notes` hits in the tree are tool config
(conformance-expected-failures.json), not metadata, and are correct as written.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: dmealing

docs/features/migrations/verified-by-retirement.md

@@ -68,7 +68,7 @@ history, and history is not what a requirement is for.
     "name": "BeatProgression", "@level": 4, "@status": "live",
     "@statement": "A scene advances when its beat completes",
     "@violation": "A scene that advances with its beat unresolved",
-    "notes": "Replaced the per-turn wall-clock timer retired in 2026-06; do not reintroduce clock-driven pacing — it advanced scenes with beats unresolved.",
+    "@notes": "Replaced the per-turn wall-clock timer retired in 2026-06; do not reintroduce clock-driven pacing — it advanced scenes with beats unresolved.",
     "@implementedBy": ["game::turn::BeatProgression"]
 }}
 ```
@@ -92,7 +92,7 @@ parent is the carrier:
     "name": "Narration", "@level": 3, "@status": "live",
     "@statement": "The narrator describes outcomes the player can act on",
     "@violation": "Narration a player cannot act on",
-    "notes": "The `sceneRecap` prompt under this requirement was retired 2026-06 and left no artifact behind — its template was deleted with it. Do not reintroduce a recap turn: it restated state the player already had and consumed a third of the budget.",
+    "@notes": "The `sceneRecap` prompt under this requirement was retired 2026-06 and left no artifact behind — its template was deleted with it. Do not reintroduce a recap turn: it restated state the player already had and consumed a third of the budget.",
     "children": [ /* the surviving child requirements */ ]
 }}
 ```