Render correct error and enable buttons when pull failed

[nightnei]

Related issues

• Fixes STU-1506

How AI was used in this PR

AI assisted me with the investigation and writing code, but the solution is mine.

Proposed Changes

This PR fixes two issues when pulling failed:

1. Before, the buttons were always disabled. This PR fixes it to enable "Disconnect/Pull" buttons after failing.
2. Before, we always printed error "Failed to check backup file size. Please try again." for any reason of failing the the pulling flow. We should at least print a real general error, e.g., "Pulling failed" or better - specific error, to help the user understand the issue at a glance and fix it w/o extra actions.

Testing Instructions

1. Create a Pressable site (I used Pressable, but teh same should work with dotcom)
2. Create a new DB table "wp_Links", so that you have both wp_links and wp_Links
3. Open Studion -> Sync -> Pull this site to Studio
4. Immediately cancel pulling
5. Assert that it's canceled (However it's not expected to have regression here, but let it be 😄)
6. Pull again
7. Wait for "Downloading backup" status and cancel
8. Assert that it's canceled well, w/o regression (it's important, since it's where we are testign new currentState?.status.key === 'cancelled' condition)
9. Pull again
10. Wait till you see an error
11. Assert that you see real error (Previously you would see Failed to check backup file size.)
    :
12. Click "Ok"
13. Assert that "Disconnect" and "Pull" buttons are enabled (Previously they were still disabled)

[wpmobilebot]

📊 Performance Test Results

Comparing 1343dc3 vs trunk

app-size

Metric	trunk	1343dc3	Diff	Change
App Size (Mac)	1271.61 MB	1271.61 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	1343dc3	Diff	Change
load	1855 ms	1873 ms	+18 ms	⚪ 0.0%

site-startup

Metric	trunk	1343dc3	Diff	Change
siteCreation	8178 ms	9177 ms	+999 ms	🔴 12.2%
siteStartup	4860 ms	4947 ms	+87 ms	🔴 1.8%

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Results are median values from multiple test runs.

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