fix(opencode): resolve console device login URL

[opencode-agent]

Summary

• resolve Console-provided device verification URLs with standard URL semantics
• prevent path-based Console deployments from duplicating /console in authorization URLs
• preserve relative paths beneath the configured server base
• reject malformed and non-HTTP(S) verification URLs as typed account service errors

Testing

• bun test test/account/service.test.ts (18 passed)
• bun typecheck
• bun x prettier --check src/account/account.ts test/account/service.test.ts
• git diff --check

Requested by: @Slickstef11 (Stefan via Slack)

[Enough1122]

AI code review — automated review for reference; please use your judgment.

No blocking issues found.

Nit: packages/opencode/src/account/account.ts:399-405 — because the base is the full server URL (${normalizedServer}/), a root-relative verification_uri_complete such as /device?user_code=… resolves to the origin root (https://host/device) rather than beneath a configured subpath (…/console/device) — standard URL semantics keep only path-relative values under /console. If self-hosted servers behind a subpath emit root-relative paths, users would land on the wrong console page and device login would look broken. Worth documenting the expectation (or normalizing root-relative paths onto the server's path prefix) once real server behavior is confirmed.