Fix three "be the customer" UI issues (padding, plans inset, search spinner)

[adalpari]

TL;DR

This PR is fixing a set of general visual errors: margins, paddings, and a loading spinner.

Description

Three small fixes found during the "Be the Customer" support rotation, all verified on-device (Jetpack, Pixel 7):

• CMM-2375 — Pre-publish social box had no internal padding. Its content (icons, text, Connect accounts / Not now) sat flush against the card edges. Added 16dp internal padding inside the box background, for both the no-connections and connected states (PostSocialSharingItem is only used in this sheet).
• CMM-2371 — Site-creation "Select a plan" screen had an extra top margin on first load (disappeared after back + reopen). Root cause: BaseAppCompatActivity already pads the window for system bars on edge-to-edge (Android 15+), and SiteCreationActivity is not excluded, but the plans fragment's Compose Scaffold + TopAppBar applied the status-bar inset again — offsetting the whole screen by the status-bar height. The first-load-vs-reopen flip was an inset-consumption race. Fixed by consuming the system-bar insets so the screen relies solely on the activity's padding, like its XML sibling screens.
• CMM-2382 — First Free Photo Library search showed no loading spinner (subsequent searches did). The loader entered the loading state still carrying the previous (empty) filter, so the picker's "hide empty view until a term is submitted" guard hid the list instead of showing the spinner. Fixed by applying the new filter together with the loading state.

Testing instructions

Pre-publish social box padding (CMM-2375):

1. Open the editor and tap Publish to open the pre-publish sheet on a site without social connections.

• Verify the social box content (icons, text, Connect accounts / Not now) has padding inside the box, not flush against its edges.

Plans screen top margin (CMM-2371):

1. Start site creation -> choose a domain -> Continue with subdomain -> theme -> continue to "Select a plan".

• Verify on first load the "Choose the perfect plan" title sits directly under the toolbar with no extra top gap (no back-and-reopen needed).

Before / After

Free Photo Library first-search spinner (CMM-2382):

1. Media -> + -> Choose from Free Photo Library -> perform your first search.

• Verify a loading spinner shows during that first search, as it does for subsequent searches.

[dangermattic]

	1 Warning
⚠️	PR is not assigned to a milestone.

Generated by 🚫 Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Android by scanning the QR code below to install the corresponding build.

	App Name	WordPress Android
	Build Type	Debug
	Version	pr23289-b8c3335
	Build Number	1498
	Application ID	org.wordpress.android.prealpha
	Commit	b8c3335
	Installation URL	16g1eefhimeoo

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Android by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Android
	Build Type	Debug
	Version	pr23289-b8c3335
	Build Number	1498
	Application ID	com.jetpack.android.prealpha
	Commit	b8c3335
	Installation URL	04g09691vcgko

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.92%. Comparing base (7eb0796) to head (b8c3335).

Additional details and impacted files

@@           Coverage Diff           @@
##            trunk   #23289   +/-   ##
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  Coverage   37.91%   37.92%           
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  Files        2352     2352           
  Lines      128795   128800    +5     
  Branches    17898    17901    +3     
=======================================
+ Hits        48836    48841    +5     
  Misses      75964    75964           
  Partials     3995     3995           

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[nbradbury]

@adalpari Changes look good! Claude flagged a potential problem.

review-pr-23289-2026-09-03.pdf

[nbradbury]

I'll go ahead and approve this and leave it to you to decide if Claude's finding is worth addressing