Add agentic Connect site flow

[bcotrim]

Related issues

• Split from Agentic UI: Site Creation #3941
• Follow-up work required in STU-1956

How AI was used in this PR

Codex assisted with repository exploration, implementation, focused regression tests, and interactive UI verification. The lifecycle and rollback boundaries, connector contracts, and light/dark presentation were reviewed and iterated during development.

Proposed Changes

• Add Connect as an Add Site path where signed-out users can log in or sign up, then find and search all relevant WordPress.com and Pressable sites with clear environment, availability, and existing-connection information.
• Create a local shell, persist its live-site relationship, and pull content into Studio with the correct rollback boundary: failures before persistence remove the shell, while later failures retain the connection for recovery.
• Focus the new local site as soon as pulling begins, open its live progress, and let the user navigate elsewhere while detailed CLI progress continues in the site status and sidebar. Start the site automatically when the pull completes.
• Remove every WordPress.com connection when a local site is deleted in Electron or local-web, with regression coverage for both paths.

Light	Dark

Testing Instructions

1. Launch the agentic UI and choose Add site → Connect while signed out. Verify both login and signup return to the Connect flow.
2. Test WordPress.com and Pressable sites. Search by name and URL, and verify available, unavailable, upgrade/transfer-required, and already-connected groups and explanations.
3. Connect an available site. Verify the shell is created without starting, the connection is saved, and Studio immediately focuses the local site with the pull status open.
4. Navigate to another site while pulling. Verify the sidebar continues to show activity and the detailed CLI pull message remains available on the connecting site.
5. Verify the site starts automatically after a successful pull and opens as a usable local copy.
6. Simulate a failure before connection persistence and verify the local shell and files are removed.
7. Simulate a pull/start failure after connection persistence and verify the local site and live relationship remain, with the failure shown in site status.
8. Delete a connected local site in Electron and local-web and verify every WordPress.com connection for that local site is removed.
9. Exercise offline, loading, empty, request-error, and retry states in light and dark color schemes.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 5755526 vs trunk

app-size

Metric	trunk	5755526	Diff	Change
App Size (Mac)	1377.87 MB	1377.91 MB	+0.05 MB	⚪ 0.0%

site-editor

Metric	trunk	5755526	Diff	Change
load	1099 ms	1080 ms	19 ms	⚪ 0.0%

site-startup

Metric	trunk	5755526	Diff	Change
siteCreation	7000 ms	6989 ms	11 ms	⚪ 0.0%
siteStartup	2352 ms	2363 ms	+11 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)