fix(gemini): resolve companion from nested node_modules in cache

[anthonyhaussman]

Summary

Fix companion plugin resolution issue affecting both opencode-gemini-auth and opencode-antigravity-auth.

When OpenCode caches companion plugins internally, it extracts them into a nested node_modules structure (e.g., ~/.cache/opencode/packages/opencode-gemini-auth@latest/node_modules/opencode-gemini-auth/dist/index.js).
Previously, the opencode-quota companion resolution logic only probed the package root without traversing into this nested node_modules directory.

This caused the resolution to fail and cache an invalid presence state when fallback resolutions were exhausted (which happens after a cache wipe).

This fix updates getRuntimePackageRoots to also yield the nested node_modules/[COMPANION_PACKAGE_NAME] path within the runtime cache directory structure, allowing the resolution logic to correctly locate and load the plugin's credentials.

Linked Issue

This resolves the bug where executing opencode-quota outside the context of a fully initialized OpenCode session (or after
wiping the .cache folder) would fail to resolve locally cached companion plugins.

OpenCode Validation

• Current production released OpenCode version tested: 1.15.3
• Why this version is relevant to the fix: The cache structure tested matches the current OpenCode caching mechanism for remote packages.

Quality Checklist

• I ran pnpm run typecheck
• I ran pnpm test
• I ran pnpm run build
• This is the smallest safe root-cause fix (no unnecessary hook/output mutation logic)
• I preserved behavioral invariants and updated/added boundary tests as needed
• I updated docs for user-facing workflow/command/config changes (README.md and CONTRIBUTING.md when applicable)
• For new API-key/token providers, I started from contributing/provider-template/ or explained why the template does not apply
• For provider setup/auth wording changes, I checked the relevant dummy .ts template in contributing/provider-template/ and verified README.md against src/lib/provider-metadata.ts (authentication/authFallbacks) and provider auth resolver/diagnostics behavior

[slkiser]

@anthonyhaussman Thanks for fix! Could I ask what model(s) you use form Gemini?

[anthonyhaussman]

@anthonyhaussman Thanks for fix! Could I ask what model(s) you use form Gemini?

@slkiser, I use the google/gemini-3.1-pro-preview model on my side. ☺️