docs(changelog): add #1507 fragment

changelog.d/1507-typed-ai-chat.md

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+- Add a typed AI chat beside the voice mic in the command dock. Replies are
+  silent and never use the microphone; messages run the same map actions as
+  voice through OpenAI Chat Completions (`OPENAI_CHAT_MODEL`) or Gemini
+  `generateContent` (`GEMINI_CHAT_MODEL`), each throttled per IP by
+  `GEV_RATELIMIT_OPENAI_CHAT_PER_MIN` or `GEV_RATELIMIT_GEMINI_CHAT_PER_MIN`
+  (default 60). The chat and voice panels minimize to a bar or dock beside the
+  right rail, and step aside for the Location and Visual Presets trays
+  (Manjunath, @manjunath22466, with Darren Dignam, @darrendignam, #1507).