Filter out internal Automattic sites from CLI wp.com sites list

[youknowriad]

Related issues

• Related to parity between Electron app and CLI site listing

How AI was used in this PR

AI identified the discrepancy between the Electron app and CLI filtering logic and made the change. The change was reviewed by a human.

Proposed Changes

• Add is_a8c field to the CLI's /me/sites API request and Zod schema
• Filter out is_a8c sites from the CLI's wp.com sites list, matching the Electron app's existing behavior in transform-sites.ts

Testing Instructions

• Run studio ai, log in, and switch to the remote sites tab (→ arrow key)
• Verify that internal Automattic sites (is_a8c) no longer appear in the list
• Verify that normal wp.com sites still appear correctly

Pre-merge Checklist

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

[wpmobilebot]

📊 Performance Test Results

Comparing f61b771 vs trunk

app-size

Metric	trunk	f61b771	Diff	Change
App Size (Mac)	1261.13 MB	1260.99 MB	0.14 MB	⚪ 0.0%

site-editor

Metric	trunk	f61b771	Diff	Change
load	1860 ms	1830 ms	30 ms	⚪ 0.0%

site-startup

Metric	trunk	f61b771	Diff	Change
siteCreation	8125 ms	8172 ms	+47 ms	⚪ 0.0%
siteStartup	4167 ms	4170 ms	+3 ms	⚪ 0.0%

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Results are median values from multiple test runs.

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