[Feature]: Add OCI Generative AI provider support

Is there an existing feature request for this?

• I have searched existing issues and feature requests, and this is not a duplicate.

Problem or Use Case

The SDK does not provide first-class support for OCI Generative AI's
OpenAI-compatible Responses API.

Users currently need to derive the regional endpoint manually, configure the
openai-project header, select the Responses API, and manage the required OCI
region and Generative AI project OCID themselves. This is error-prone and makes
OCI-backed OpenHands deployments difficult to configure reliably.

Related upstream issue: OpenHands/OpenHands#17512.

Desired Behavior

Add an oci_genai/<model-id> provider route that:

• accepts an OCI region, Generative AI project OCID, and API key;
• derives the regional OCI /openai/v1 endpoint;
• adds the required openai-project request header;
• uses the OpenAI-compatible Responses API;
• supports normal responses and tool calls; and
• exposes the provider-specific fields through the Agent Server schema.

Acceptance Criteria

• oci_genai/<model-id> is recognized as a first-class provider route.
• OCI region and Generative AI project OCID are validated.
• The regional /openai/v1 endpoint is derived automatically.
• The openai-project header is added automatically.
• Normal Responses API output and function tool calls are supported.
• Provider fields survive profile serialization and secret handling.
• Automated tests cover validation, request construction, normal responses, and tool calls.

Alternatives Considered

Users can configure OCI through the generic OpenAI-compatible provider path,
but this requires manually constructing the endpoint and headers and does not
provide validation for the required OCI-specific values.

Priority / Severity

Medium - Would improve experience

Estimated Scope

Unknown - Not sure about the technical complexity

Feature Area

• Agent API / Core functionality
• Tools / Tool system
• Skills / Plugins
• Agent Server
• Workspace management
• Configuration / Settings
• Examples / Templates
• Documentation
• Testing / Development tools
• Performance / Optimization
• Integrations (GitHub, APIs, etc.)
• Other

Technical Implementation Ideas (Optional)

No response

Additional Context

No response

No files or tests are named. Start by locating the existing provider-route registration, Agent Server configuration schema, profile serialization and secret handling, and OpenAI-compatible Responses API tests. Done means an OCI route validates its region and project OCID, builds the regional endpoint and header, supports responses and tool calls, and has automated coverage for the listed acceptance criteria.