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>

docs/CHANGELOG.md

@@ -29,6 +29,13 @@ Honorific integration).
 - Plugin-load profiling logs stay on: `MessageStore.Connect`, `MessageStore.Migrate`, `FilterAllTabs` and the
   auto-translate warm-up timing log are now Information level rather than Debug. They serve as a tripwire so a
   future regression past 100 ms shows up directly in `/xllog` without re-enabling Debug.
+- 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. Third-party
+  integrations that historically only subscribe to ChatTwo's IPC — for example Artisan's and AllaganTools'
+  context-menu hooks — 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).
 - Internal: hypothesis-triage during the R2 cycle falsified three of the four candidate root causes
   (font-atlas sync, theme-apply ABGR-cache init, multiple-window render). Actual cause is `DrawList` setup