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>

HellionChat/HellionChat.yaml

@@ -56,6 +56,17 @@ changelog: |-
       (MessageStore connect/migrate, FilterAllTabs, auto-translate
       warmup) as a regression tripwire — a future load past 100 ms
       will show up in /xllog without a Debug filter.
+    - 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).
 
     Based on Chat 2 1.35.3 (upstream Infiziert90/ChatTwo, EUPL-1.2).