Fetch every page of syncable sites and mark already-connected ones

[shaunandrews]

Related issues

• Part of the site-creation onboarding redesign — see the umbrella PR (linked below once open) for the full plan.

How AI was used in this PR

Split out of the workbench/site-creation exploration branch with Claude Code; designed and tested by Shaun on the original branch.

Proposed Changes

• Users with many WordPress.com sites were only seeing a subset in the site picker: the unpaginated v1.2 /me/sites request silently truncated results. The fetch now drains every page via the v1.3 endpoint, so the full account is always available.
• Sites that are already connected to a local site are now marked as such, so pickers can show an "already connected" state instead of offering them again.

Testing Instructions

• With a WordPress.com account that has more than 100 sites, open the sync "Connect site" modal — every site should be listed.
• Connect a site, then reopen the picker — the connected site should appear as already connected.

Pre-merge Checklist

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

[wpmobilebot]

📊 Performance Test Results

Comparing 7e00f62 vs trunk

app-size

Metric	trunk	7e00f62	Diff	Change
App Size (Mac)	1354.73 MB	1354.73 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	7e00f62	Diff	Change
load	1643 ms	1662 ms	+19 ms	⚪ 0.0%

site-startup

Metric	trunk	7e00f62	Diff	Change
siteCreation	9035 ms	9049 ms	+14 ms	⚪ 0.0%
siteStartup	4403 ms	4404 ms	+1 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

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

[youknowriad]

This doesn't feel great to me. We shouldn't be fetching unpaginated results, there's a risk here depending on the number of sites of a given user. Instead I believe it's better to have a UI that is either paginated or load on scroll or things like that.