Implement Together AI adapter

[op-simoneromeo]

Summary

• replace the ai-together stub with a Together AI OpenAI-compatible chat-completions adapter
• use the documented https://api.together.ai/v1/chat/completions route with TOGETHER_API_KEY
• support dry-run, system/user messages, max_tokens/temperature, stream=false, extra passthrough params, usage mapping, text-choice fallback, custom baseUrl, and provider error excerpts
• add mocked fetch tests for dry-run, request shape, response mapping, compatible text choices, and error handling

Validation

• corepack pnpm@9.12.0 exec vitest run packages/ai/together/src/index.test.ts
• corepack pnpm@9.12.0 --filter @profullstack/sh1pt-ai-together typecheck
• corepack pnpm@9.12.0 --filter @profullstack/sh1pt-ai-together build
• git diff --check
• common secret-pattern scan over changed Together files

No real Together API key or other production secret was used; tests mock fetch.

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.