feat(telemetry): add canonical GenAI provider names

[dialupdisaster]

Summary

• normalize known opencode provider IDs to canonical gen_ai.provider.name values
• preserve unknown and custom provider IDs unchanged
• add the canonical attribute to LLM spans and api_request/api_error logs without changing existing raw provider attributes
• cover Bedrock, Azure OpenAI, Gemini, Vertex AI, Mistral AI, xAI, and fallback behavior

This also provides a shared genAiProviderName helper for GenAI metrics such as the histogram proposed in #102.

Testing

• bun run typecheck
• bun test (311 passing)
• bun run lint
• bun run check:jsdoc-coverage
• git diff --check

[github-actions]

• [P2] src/util.ts:27 — Plain-object lookup includes inherited properties. Custom IDs such as __proto__, constructor, or toString return non-string prototype values instead of being preserved, producing invalid OTel attributes. Use an own-property check, null-prototype object, or Map, and add a regression test.

Unable to run checks because bun is unavailable in this environment.