feat(ai): MiniMax full-stack — embeddings compat shim, asymmetric type, chat touchpoint

[tcflying]

Problem

The minimax recipe declared only an embedding touchpoint and was tagged
openai-compatible, but MiniMax's /v1/embeddings endpoint is not OpenAI-shaped
at the wire level — it requires {model, texts, type} and returns
{vectors, base_resp}. With no fetch shim, the AI SDK sent {input} and MiniMax
replied status_code 2013 "missing required parameter texts", surfacing as
[embed(minimax:embo-01)] Invalid JSON response and Embedded 0 chunks. MiniMax was
effectively unusable for embeddings, and there was no chat touchpoint at all.

Fix (3 commits)

1. gateway.ts — minimaxCompatFetch (mirrors voyageCompatFetch /
   zeroEntropyCompatFetch): OUTBOUND maps input → texts, derives type from the
   threaded input_type, strips OpenAI-only keys; INBOUND rewrites
   {vectors} → {data:[{embedding,index}]} and surfaces a non-zero
   base_resp.status_code as a thrown error (MiniMax returns HTTP 200 on logical
   errors). Wired into instantiateEmbedding's fetchWrapper dispatch for
   recipe.id === 'minimax'.
2. dims.ts — asymmetric retrieval. embo-01 now emits input_type (same seam as
   ZE/Voyage) instead of a hardcoded type:'db', so embedQuery() threads 'query'
   and embed() threads 'document'; the shim maps that to MiniMax's type: db|query
   wire field.
3. recipes/minimax.ts — chat touchpoint. MiniMax exposes an OpenAI-compatible
   /v1/chat/completions endpoint (same key); M3 function-calls and returns
   OpenAI-shaped responses (no shim needed). Adds MiniMax-M3 / MiniMax-M2.7
   (supports_tools, 800K ctx). With this plus the embedding fix, gbrain runs
   end-to-end — embed + search + graph + chat synthesis — on MiniMax alone, no
   OpenAI/Anthropic key required.

Testing

• Verified end-to-end against the live API with a coding-plan key: embo-01 embeds
  (1536d), asymmetric db/query both succeed, gbrain think synthesizes from a
  brain page with a citation (Model: minimax:MiniMax-M3).
• test/ai/recipe-minimax.test.ts updated for the new input_type behavior (document
  default + query path) and a new chat-touchpoint assertion.
• Green locally: recipe-minimax, recipes-existing-regression, gateway,
  gateway-chat, dims-openai, dims-zeroentropy (89+ tests, 0 fail);
  bun run typecheck clean.

🤖 Generated with Claude Code

[tcflying]

Added one more commit (fix(cli): windowsHide on the startup check-update spawn): the detached check-update --refresh-cache refresh had no windowsHide, so on Windows it flashed a console window / launch-error dialog. Same spawn-hygiene class. Happy to split into its own PR if you'd prefer it separate from the MiniMax work.