feat(sdk): support per-user Vercel Connect subjects

[HugoRCD]

Summary

• GithubConnectParams now accepts a subject; the default stays { type: 'app' } (the project's GitHub App installation), so nothing changes for existing consumers.
• In the eve extension, connect.subject also accepts a per-caller resolver called with the tool execution context on every call — e.g. (ctx) => ({ type: 'user', id: ctx.session.auth.current!.principalId }). Multi-user apps where each user connects their own GitHub account can now mint each caller's own connection token instead of routing everyone through the shared app installation. A caller without an active connection gets UserAuthorizationRequiredError from Connect rather than silently falling back to the app token.
• The extension threads the eve ToolContext from execute into token resolution; the token is minted lazily, per tool call. The durable-callback AST guard still passes — callbacks stay inline and only gain the ctx parameter.

Docs updated (Vercel Connect guide "Per-user tokens", eve extension page, API reference, published skill, extension README) plus a minor changeset for both packages.

Test plan

• pnpm build, pnpm lint, pnpm typecheck, pnpm test all green (91 SDK tests, extension AST guard)
• New test: explicit user subject passes through to getToken instead of the app default
• Real-world check in a multi-user eve template: multi-step turn with a GitHub tool using the per-caller resolver

[vercel]

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Project	Deployment	Actions	Updated (UTC)
github-tools-docs	Ready	Preview, v0	Aug 31, 2026 2:58pm
github-tools-test-agent	Ready	Preview, v0	Aug 31, 2026 2:58pm

[github-actions]

Thank you for following the naming conventions! 🙏