docs: surface the ChatTwo IPC compatibility layer in v1.4.9 patch notes

Adds a "ChatTwo IPC compatibility layer" bullet across all six
release-note surfaces so the new behaviour from commits 8c4afaa and
655c903 is visible to users via the manifest installer, the Gitea
release page, the README project-status section, the changelog/roadmap
docs and the Forge-Discord announcement.

Files touched:
- HellionChat/HellionChat.yaml: bullet added inside the v1.4.9
  changelog block, preserved order so the regression-tripwire line
  still comes before the migration-stays line.
- repo.json: Changelog field kept synchronous (JSON-escaped newlines).
- README.md: project-status paragraph extended with a one-sentence
  recap of the IPC mirror and the conflict-detection caveat.
- docs/CHANGELOG.md: bullet inserted between the profiling-logs and
  migration-stays bullets, code-fenced gate names.
- docs/ROADMAP.md: v1.4.9-released section gets the same recap so the
  cycle history stays self-describing.
- .github/forge-posts/v1.4.9.md: German-only bullet for the Discord
  embed, slotted before the migration-v17 bullet. Char-cap holds —
  preflight Block C reports the embed total well under 5500 chars.

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

README.md

@@ -296,8 +296,14 @@ is invisible inside the post-reload font-atlas build window. Slash commands `/he
 their target window is opened the first time. The configuration-button entry in Dalamud's plugin manager hangs on
 the same path. Three plugin-load profiling logs (auto-translate warm-up, message-store connect, tab filter) stay
 on at Information level as a regression tripwire — if a future change pushes the load past 100 ms again, the cost
-is right there in `/xllog`. Migration v17 stays (no schema bump). Tenth sub-patch of the v1.4.x polish sweep
-series (as of 2026-05-15).
+is right there in `/xllog`. The release also ships a ChatTwo IPC compatibility layer: HellionChat now mirrors
+ChatTwo's full IPC surface (`GetChatInputState`, `ChatInputStateChanged`, `Register`, `Unregister`, `Available`,
+`Invoke`) under the `ChatTwo.*` namespace in addition to our existing `HellionChat.*` provider gates, so
+third-party integrations that historically only subscribe to ChatTwo's IPC (Artisan's and AllaganTools' context-
+menu hooks are the practical examples) keep working without requiring a code change on their side. Conflict
+detection prevents ChatTwo from loading in parallel with HellionChat, so there is no slot-collision risk at
+runtime. Migration v17 stays (no schema bump). Tenth sub-patch of the v1.4.x polish sweep series (as of
+2026-05-15).
 
 Hellion Chat is a standalone plugin, no longer a fork in the repository sense. Fully completed: