chore(release): v0.2.1

Bump all version carriers (plugin.json, package.json, README badge,
SKILL.md frontmatter) and record the release in the changelog.

Also backfills the missing [0.2.0] changelog section: that release shipped
without one, which would have left the changelog jumping 0.1.0 -> 0.2.1.
Content reconstructed from the v0.2.0 commit, not from its subject line.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CvTviFeoMCKJcALATRempy

CHANGELOG.md

@@ -5,6 +5,47 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.1] - 2026-07-25
+
+### Fixed
+
+- Broadcast self-delivery: `coord-send --broadcast` left no seen-set entry for
+  the sender, so the announcing repo got its own announcement injected at its
+  next session start. The delivered filename is now recorded in
+  `_broadcast/seen/<sender>` at delivery time, reusing the existing per-repo
+  seen set rather than adding a second exclusion mechanism. Filtering on the
+  `from:` field at read time was rejected: `from:` is sender-controlled, so it
+  would let any repo suppress a broadcast for another by forging the field.
+  The seen file is keyed by the raw sender name (the read side keys it
+  unsanitized, so the two must agree); senders containing a slash, or equal to
+  `.`/`..`, skip the marking rather than escape the directory.
+
+### Added
+
+- Selftest: 64 -> 68 checks, covering sender self-exclusion, unaffected
+  delivery to other repos, self-exclusion for sender names that are not
+  shell-clean, and the seen-marking path-escape guard.
+
+## [0.2.0] - 2026-07-24
+
+Hardening pass over the three CLIs.
+
+### Fixed
+
+- Atomic delivery: the temp file is created inside the destination directory
+  (dot-prefixed, invisible to the inbox glob), so the final rename never
+  crosses filesystems and readers never observe a half-written message.
+- `.` and `..` are rejected explicitly in the `--reply-to` and `coord-done`
+  name guards instead of relying on downstream failure.
+
+### Added
+
+- `-h`/`--help` on `coord-inbox.sh`, making usage output uniform across the
+  three CLIs.
+- Selftest: 48 -> 64 checks, closing gaps around the default mailbox path via
+  `HOME` fallback, malformed frontmatter on the read path, and a read-only
+  destination directory.
+
 ## [0.1.0] - 2026-07-24
 
 First public release: extraction of a battle-tested personal mechanism into a