fix(tui): hide error hint when MCP Enter starts sign-in

[kitlangton]

Why

Since #48939, needs_auth MCP servers carry a required error reason. That made statusError() treat them as error-bearing, so the dialog footer rendered enter to view error for servers like stripe or uidotsh. But Enter does not open an error view for these servers: when the server has an integration, it starts the sign-in flow. The hint was wrong.

What Changes

The footer hint now matches what Enter actually does:

Server state	Before	After
needs_auth with integration (e.g. stripe)	enter to view error sign in space	sign in space
needs_auth without integration	enter to view error space	unchanged — Enter still opens the error details
failed	enter to view error space	unchanged

Before: MCP servers dialog for a sign-in-gated server shows enter to view error even though Enter opens sign-in.

After: the footer only offers sign in space.

Demo

Side-by-side recording of the same fixture MCP server (a remote endpoint returning 401, so it lands in needs_auth with an integration) against the pre-fix baseline (left, BEFORE mark) and this branch (right, AFTER mark). Both run the identical /mcps dialog; only the footer hint differs. See the attached mcp-footer-before-after.mp4.

Scope

This PR only changes the focused-server footer logic in DialogMcp. The Needs authentication: <reason> line in the server status dialog is informational and intentionally unchanged.

Verification

cd packages/tui
bun run test test/cli/tui/dialog-mcp.test.tsx
bun typecheck

• The regression test fails on v2 with the exact footer from the bug report (enter to view error sign in space) and passes with the fix.
• bun run check from the repo root: lint + typecheck clean (also enforced by the pre-push hook).
• Manual Drive recording above compares v2 vs this branch against a live 401 MCP endpoint.

mcp-footer-before-after.mp4