Add data-group attribute to service groups

[goulimis]

Proposed change

Adds data-group="<name>" to each service group's wrapper <div>, mirroring the data-name attribute services already get. Lets custom CSS/JS target a specific group by name without any config-schema changes. One line, purely additive.

Solution by me, code by Claude Code.

Closes #6729

Type of change

• New service widget
• Bug fix (non-breaking change which fixes an issue)
• New feature or enhancement (non-breaking change which adds functionality)
• Documentation only
• Other (please explain)

Checklist:

• If applicable, I have added corresponding documentation changes.
• If applicable, I have added or updated tests for new features and bug fixes (see testing).
• If applicable, I have reviewed the feature / enhancement and / or service widget guidelines.
• I have checked that all code style checks pass using pre-commit hooks and linting checks.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• In the description above I have disclosed the use of AI tools in the coding of this PR.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.91%. Comparing base (fc696a1) to head (106d663).
⚠️ Report is 64 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/components/services/group.jsx	0.00%	0 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (100.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #6880      +/-   ##
==========================================
- Coverage   81.92%   81.91%   -0.01%     
==========================================
  Files         537      537              
  Lines        9691     9692       +1     
  Branches     1812     1813       +1     
==========================================
  Hits         7939     7939              
  Misses       1051     1051              
- Partials      701      702       +1     

Flag	Coverage Δ
vitest-shard-1	27.06% <0.00%> (-0.01%)	⬇️
vitest-shard-2	20.58% <0.00%> (-0.01%)	⬇️
vitest-shard-3	28.86% <0.00%> (-0.01%)	⬇️
vitest-shard-4	22.76% <0.00%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
src/components/services/group.jsx	77.77% <0.00%> (-3.00%)	⬇️

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