Add OCI Enterprise AI Chat asset

[ralungei]

Summary

Adds a new asset under ai/gen-ai-agents/oci-enterprise-ai-chat/: a Next.js 16 + React 19 chat interface for OCI Enterprise AI.

Features:

• Streaming chat against OCI Responses API
• MCP tool integration (OAuth 2.1 PKCE, OAuth 2.0 client credentials, API key, bearer)
• IDCS SSO via OAuth 2.0 Authorization Code
• File search (RAG) over OCI vector stores with chunk-level citations
• Native OCI tools: Code Interpreter, File Search
• Customizable appearance (white-label: title, logo, accent color), dark mode
• Settings workbench: prompts, tools, memory, observability, appearance
• Dockerfile + deployment guide for OCI Container Instance behind a Load Balancer

License: UPL v1.0

Note: superseding closed PR #2954 (fork-based, OCA bot stuck). Same content, opened from a branch on this repo directly per the suggested workflow.

Test plan

• Asset folder follows the Area/Sub-Area/Asset structure (ai/gen-ai-agents/oci-enterprise-ai-chat/)
• LICENSE file present (UPL v1.0, year 2026)
• README.md at the asset root explains purpose, configuration, and deployment
• No real emails, secrets, OCIDs, or internal IPs in any file
• No links to internal Oracle systems (Confluence, Slack, OraHub, etc.)
• All content classified as Public