chore(release): stamp 0.2.1 release narrative with commit hash 3ae4012

Records the 0.2.1 release commit hash in the release_commit frontmatter
field of changelog/releases/0.2.1.md, mirroring the stamp pass done for
0.2.0. The narrative now points at the exact commit the release was cut
from.

Files changed:
- changelog/releases/0.2.1.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mpstaton

changelog/releases/0.2.1.md

@@ -23,7 +23,7 @@ augmented_with: Claude Code (Opus 4.7, 1M context)
 release_tag: "0.2.1"
 release_url: "https://github.com/lossless-group/perplexed-plugin/releases/tag/0.2.1"
 prior_release_tag: "0.2.0"
-release_commit: "pending — stamp after the release commit"
+release_commit: "3ae4012"
 ---
 
 ## Why care?