feat(oracle): add Cohere embeddings support

[fede-kamel]

Summary

Adds the Oracle GenAI embeddings endpoint (Cohere embed models on OCI) and wires it into the gateway's /v1/embeddings surface.

This is the embeddings split from the original #1537 (per @narengogi's review asking to trim into focused PRs). #1537 now contains only the streaming tool-call fix.

What changed

File	Change
src/providers/oracle/embed.ts	New — request transform + OCI-to-OpenAI response transform
src/providers/oracle/api.ts	Route the embed endpoint to OCI /actions/embedText
src/providers/oracle/index.ts	Wire OracleEmbedConfig + OracleEmbedResponseTransform
src/providers/oracle/embed.test.ts	New — focused unit tests

Total diff: +266 / -0, 4 files, all under src/providers/oracle/.

Behaviour

• Input shaping: handles OpenAI's input as string, string array, or object array ({text: ...}).
• input_type: maps OpenAI-style values (search_document, search_query, classification, clustering, image) to OCI's uppercase enum.
• truncate: maps none / start / end to OCI's NONE / START / END.
• Serving mode: ON_DEMAND only in this PR. DEDICATED can follow once a matching oracleEndpointId provider option lands (intentionally out of scope here to keep the PR focused).
• Response: maps OCI embeddings: number[][] + inputTextTokenCount to OpenAI's data: [{embedding, index}] + usage.

Verified

• npm run build ✓
• npm run format:check ✓
• Type-clean (tsc --noEmit reports no errors in src/providers/oracle/)
• Verified live against inference.generativeai.us-chicago-1.oci.oraclecloud.com/20231130/actions/embedText for cohere.embed-multilingual-v3.0 (single string, batch, search_document type).

Related

• Split from fix(oracle): emit tool_calls in streaming responses #1537 per @narengogi's review
• Supersedes feat(oracle): Add rerank and guardrails support #1540 (the embeddings portion). The old PR carried a heavier change set that bundled handler dispatch and modelConfig.ts; this PR is the trimmed-down equivalent focused solely on the /v1/embeddings surface.
• Sibling: fix(oracle): emit tool_calls in streaming responses #1537 (streaming tool-call fix), fix(oracle): route maxTokens to maxCompletionTokens for GPT-5 family #1635 (GPT-5 maxCompletionTokens routing). The multi-vendor handler dispatch work that was originally bundled is parked for a separate focused PR.

[fede-kamel]

@roh26it @narengogi @VisargD — companion to #1537. Rebased on main, mergeable, e2e-verified live against cohere.embed-multilingual-v3.0 on us-chicago-1. Diff is +266 / −0, all under src/providers/oracle/ plus a one-line embed route case in api.ts. See #1537 for the broader context on bringing the OCI provider quality up to par. Happy to take review feedback.

[fede-kamel]

Thanks for the review @narengogi! What's the next step from here to land this in a release? Happy to add a changelog entry, rebase, or anything else the merge process needs — just let me know what's missing.