Scope preview list --format json output to the authenticated user

[bcotrim]

Related issues

• N/A

How AI was used in this PR

Implemented and verified with Claude Code under my direction; I reviewed the diff and the direction was agreed beforehand.

Proposed Changes

Preview snapshots are per-user by design, but studio preview list --format json returned before the auth check and dumped every snapshot in cli.json unfiltered. A logged-out user (or a different account on the same machine) could see preview sites they don't own.

• The json path now behaves like the table path: snapshots are filtered by the authenticated user's ID.
• When logged out it emits an empty array ([]) instead of erroring, so the desktop app degrades gracefully
• Site scoping is unchanged: json output still covers all local sites, and --all semantics are untouched.

Testing Instructions

1. npm run cli:build
2. Create a site + preview(s) site or use existing ones
3. While logged in (node apps/cli/dist/cli/main.mjs auth status): run node apps/cli/dist/cli/main.mjs preview list --format json — your snapshots are listed.
4. Log out (auth logout) and run the same command — output is [] with exit code 0, no error.

Pre-merge Checklist

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

[wpmobilebot]

📊 Performance Test Results

Comparing 377e03f vs trunk

app-size

Metric	trunk	377e03f	Diff	Change
App Size (Mac)	1355.69 MB	1355.69 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	377e03f	Diff	Change
load	1078 ms	1109 ms	+31 ms	⚪ 0.0%

site-startup

Metric	trunk	377e03f	Diff	Change
siteCreation	7024 ms	6984 ms	40 ms	⚪ 0.0%
siteStartup	2357 ms	2353 ms	4 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

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

[nightnei]

LGTM, works as expected and I confirm that in trunk it wasn't gated and now it works well