fix(theme): fill NFS catalog entity tab content well

[ciiay]

Description

On NFS catalog entity pages, Topology and Scorecard sat in a short BUI Container inside a tall <main>, leaving an empty band in the page well. Theme 1.0.2 already sized SidebarPage > main, but main stayed display: block, so the nested container’s flex: 1 never grew.

This makes classless BUI <main> (not Backstage Page, which uses display: grid) a flex column so those tabs fill the well.

Fixed

• RHDHBUGS-3543 — [NFS] Empty gap below #root on Catalog entity tabs (Topology / Scorecard)

Checklist

• A changeset describing the change and affected packages. (more info)
• Added or Updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)

Verified on app-next, via redhat-developer/rhdh#5115:

[rhdh-gh-app]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@red-hat-developer-hub/backstage-plugin-theme	workspaces/theme/plugins/theme	patch	v1.0.2

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.61%. Comparing base (db8ab88) to head (c8d7f17).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4418   +/-   ##
=======================================
  Coverage   61.61%   61.61%           
=======================================
  Files        2541     2541           
  Lines      101911   101911           
  Branches    28557    28557           
=======================================
  Hits        62788    62788           
  Misses      37289    37289           
  Partials     1834     1834           

Flag	Coverage Δ		*Carryforward flag
adoption-insights	84.55% <ø> (ø)		Carriedforward from db8ab88
ai-integrations	67.70% <ø> (ø)		Carriedforward from db8ab88
app-defaults	48.37% <ø> (ø)		Carriedforward from db8ab88
augment	46.67% <ø> (ø)		Carriedforward from db8ab88
boost	79.84% <ø> (ø)		Carriedforward from db8ab88
bulk-import	72.79% <ø> (ø)		Carriedforward from db8ab88
cost-management	13.55% <ø> (ø)		Carriedforward from db8ab88
dcm	72.09% <ø> (ø)		Carriedforward from db8ab88
e2e-adoption-insights	60.00% <ø> (ø)		Carriedforward from db8ab88
e2e-extensions	62.13% <ø> (ø)		Carriedforward from db8ab88
e2e-global-header	49.45% <ø> (ø)		Carriedforward from db8ab88
e2e-homepage	43.49% <ø> (ø)		Carriedforward from db8ab88
e2e-intelligent-assistant	46.68% <ø> (ø)		Carriedforward from db8ab88
e2e-orchestrator	49.51% <ø> (ø)		Carriedforward from db8ab88
e2e-quickstart	55.21% <ø> (ø)		Carriedforward from db8ab88
e2e-scorecard	50.21% <ø> (ø)		Carriedforward from db8ab88
e2e-theme	16.36% <ø> (ø)		Carriedforward from db8ab88
extensions	56.59% <ø> (ø)		Carriedforward from db8ab88
global-floating-action-button	71.18% <ø> (ø)		Carriedforward from db8ab88
global-header	66.50% <ø> (ø)		Carriedforward from db8ab88
homepage	47.46% <ø> (ø)		Carriedforward from db8ab88
install-dynamic-plugins	58.57% <ø> (ø)		Carriedforward from db8ab88
intelligent-assistant	75.35% <ø> (ø)		Carriedforward from db8ab88
konflux	91.98% <ø> (ø)		Carriedforward from db8ab88
lightspeed	69.02% <ø> (ø)		Carriedforward from db8ab88
mcp-integrations	83.40% <ø> (ø)		Carriedforward from db8ab88
orchestrator	70.92% <ø> (ø)		Carriedforward from db8ab88
quickstart	63.74% <ø> (ø)		Carriedforward from db8ab88
sandbox	79.56% <ø> (ø)		Carriedforward from db8ab88
scorecard	87.36% <ø> (ø)		Carriedforward from db8ab88
theme	88.91% <ø> (ø)
translations	5.12% <ø> (ø)		Carriedforward from db8ab88
x2a	79.20% <ø> (ø)		Carriedforward from db8ab88

*This pull request uses carry forward flags. Click here to find out more.

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[logonoff]

Can you check this isn't fixed by #2800

[ciiay]

Can you check this isn't fixed by #2800

Thanks for the comment. The other PR won't cover the fix of this bug. That PR adds BUI PatternFly tokens and chrome (page-inset borders, hide duplicate PluginHeader, .bui-Container { max-width: none }). The closest layout rule is height: 100vh on BackstageSidebarPage when there is a nav and no Backstage Page. That is the same kind of shell fill as theme 1.0.2. It does not make <main> a flex column. The gap I verified was: main 880px / display: block, Topology bui-Container 252px / flex: 1 1 0%. Flex-grow never ran. #2800 never touches main’s display.