feat: complete OpenCode V2 parity and endpoint routing - #144

What changed

• Completes catalog metadata and context-tier mapping while preserving OpenCode V1 behavior and adding V2 provider transforms plus key/environment auth.
• Routes models by the endpoint metadata refreshed by catalog sync, including same-CLI-version refreshes; avoids timestamp-only catalog changes.
• Removes the redundant manual provider block from the repo config and updates the README/spec with current V1/V2 setup and plan limits.

Validation

• bun run check passed: 235 tests, 668 assertions, lint, format, and typecheck.
• bun run build and bun run verify:release-candidate passed.
• Isolated official Docker checks: V1.18.30 listed 82 models; V2.0.18 listed the same 82 through /api/model and exposed key/env integration methods. DeepSeek V4 Flash returned OK in V2; Responses routing passed local mock-stream checks in both versions.
• A GOAT-key Claude Sonnet 4.6 request returned MODEL_NOT_IN_PLAN (Pro and above or extra on-demand usage). Entitled Claude inference remains unverified; the docs ask users with access to open an issue or PR if routing fails.

The active global OpenCode config and auth files were not changed.