Implement Akash ML chat adapter

[op-simoneromeo]

Summary

• replace the Akash ML placeholder with an OpenAI-compatible chat completions adapter
• add current AkashML/chatapi defaults, model list, dry-run behavior, usage mapping, and setup docs
• cover request mapping, dry-run, compatible response fallback, and error excerpts in tests

Validation

• pnpm vitest run packages/ai/akashml/src/index.test.ts
• pnpm --filter @profullstack/sh1pt-ai-akashml typecheck
• pnpm --filter @profullstack/sh1pt-ai-akashml build
• git diff --check
• secret-pattern scan over packages/ai/akashml found no matches

No real API key or other secret was used or committed.