Agentic UI: Port selective sync

[nightnei]

Related issues

• Fixes STU-1946

How AI was used in this PR

Claude Code assisted with mapping the legacy selective-sync implementation via a few iterations. All changes were reviewed and visually verified by hand in both color schemes.

Proposed Changes

As agreed in STU-1946, the Agentic UI adopts the classic UI's Selective Sync as-is for the beta, so both UIs offer the same sync capabilities.
To keep review easy, the legacy modules were intentionally copied verbatim into apps/ui/src/components/selective-sync/.
Note, there is an existing issue in trunk - UI says that the Push is finished, hovewer it isn't. This issue is not covered in this PR - DOTPROD-170.

Testing Instructions

1. Open Agentic UI, connect a site to a local site
2. Click on Pull and Push and assert that the dialog looks completely the same as in Classic UI and selection works well in the tree

3. Try to pull all data or select for example only `themes` folder and assert that it works well. 4. You can test the push action too; it works, but there is an existing bug which is not covered in this PR (DOTPROD-170).

[shaunandrews]

We'll iterate on the UI more once this merges, but the only thing we should consider is adding a max-width to the modal to avoid these huge line-lengths:

[nightnei]

We'll iterate on the UI more once this merges, but the only thing we should consider is adding a max-width to the modal to avoid these huge line-lengths:

Limited to 960px

[wpmobilebot]

📊 Performance Test Results

Comparing 4c755e9 vs trunk

app-size

Metric	trunk	4c755e9	Diff	Change
App Size (Mac)	1402.77 MB	1373.14 MB	29.63 MB	🟢 -2.1%

site-editor

Metric	trunk	4c755e9	Diff	Change
load	1058 ms	1038 ms	20 ms	⚪ 0.0%

site-startup

Metric	trunk	4c755e9	Diff	Change
siteCreation	7536 ms	7032 ms	504 ms	🟢 -6.7%
siteStartup	2868 ms	2388 ms	480 ms	🟢 -16.7%

---

Results are median values from multiple test runs.

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

[katinthehatsite]

😮

That is to say that I started the review and checking this now

[katinthehatsite]

What happens if I start the sync process in the new UI, then switch to the classic UI? So far, I am seeing no sync progress in the classic UI in that case and I can start again the sync from there? I think I expected the sync progress to be reflected even if I change between the UI mid-process. What do you think?

[katinthehatsite]

I think it would be nice if these links had color even if they don't in the old UI:

(the one at the end that has Create a new backup)

[katinthehatsite]

Another observation is that I was able to delete the local site mid-sync e.g. while pushing. Would the delete option be disabled when the push is happening to prevent sync errors?