fix(e2e): configure preview keys through credential dialogs

[FradSer]

Summary

Update the Preview smoke-test credential helper to fill the current Add Key dialog, then ensure the newly created credential is the provider's default.

Why

The helper still searches the provider card for fields and an obsolete checkbox that moved into a dialog. The smoke test times out before reaching Preview. Looking only for any Default badge can also reuse an older credential. Scope the form to its dialog and default selection to the new credential row.

Related to the dialog and console work in #617 and #621. Extracted from #693 following review request 6. Existing issues and PRs were searched; no dedicated open issue was found. No issue is closed by this PR.

Verification

• just e2e e2e/cases/ui/preview-credential-dialog.spec.ts with a local external config selecting installed Chrome: 2 passed.
• Deterministic GraphQL fixtures cover both first credential and existing-default cases, including the mutation inputs and selected default. No real provider credential or API is used.
• Red/green: the former card locator fails; the new helper passes. The existing-default case also reproduced a broad Default locator failure before row scoping.
• just tc-package @mosoo/e2e; just lint; just commit-check: passed.
• Exact-head just check was attempted on local Linux (Bun 1.4.0): format/docs/lint/type stages passed; unchanged Driver tests had three failures (backpressure plus ACK-unknown terminal creation and committed-file lifecycle timeouts; 2,279 passed / 47 skipped / 3 failed). This initial full-gate failure is retained, not claimed as a pass.
• Fresh browser acceptance passed 2/2 again. All three failed Driver cases pass in isolation (3/3); their identical source also passed the complete #699 hosted gate. No Driver change is included.
• Full hosted CI is triggered by Ready for review; see Checks for this PR’s own result. Real-provider Preview smoke was not run.

Review

• Closest review areas: configureProviderCompanyKey and its isolated browser regression cases.
• Env/config changes: N/A; external local browser config is not committed.
• Known trade-offs: online model behavior is outside these credential-dialog fixture cases.

Impact

• Generated files / GraphQL / DB / lockfile: N/A; unchanged.
• Risk and rollback: revert this isolated commit. No deployment or migration.

Design

N/A: no product UI changes.