feat(variables): add external secrets pages

[rmnbrd]

Summary

⚠️ Based on #2720

Adds the full external secrets variables UI after creation: dedicated external secret tabs/pages, service variable tabs, associated external secrets modal, generalized associated-items modal, route restructuring, tests/snapshots, and related UI polish.

Screenshots / Recordings

Testing

• Changes tested locally in the relevant Console's pages and Storybooks
• yarn test or yarn test -u (if you need to regenerate snapshots)
• yarn format
• yarn lint

PR Checklist

• I followed naming, styling, and TypeScript rules (see .cursor/rules)
• I performed a self-review (diff inspected, dead code removed)
• I titled the PR using Conventional Commits with a scope when possible (e.g. feat(service): add new Terraform service) - required for semantic-release
• I only kept necessary comments, written in English (watch for useless AI comments)
• I involved a designer to validate UI changes if I am not a designer
• I covered new business logic with tests (unit)
• I confirmed CI is green (Codecov red can be accepted)
• I reviewed and executed locally any AI-assisted code

[Copilot]

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[codecov]

Codecov Report

❌ Patch coverage is 55.92417% with 186 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.43%. Comparing base (ad0a150) to head (44e0ca4).

Files with missing lines	Patch %	Lines
...es/feature/src/lib/variable-list/variable-list.tsx	49.51%	36 Missing and 16 partials ⚠️
.../src/lib/external-secrets/external-secrets-tab.tsx	61.06%	38 Missing and 13 partials ⚠️
...cret-manager-associated-external-secrets-modal.tsx	78.57%	13 Missing and 5 partials ⚠️
...ce-variables-tabs/service-variables-custom-tab.tsx	40.74%	15 Missing and 1 partial ⚠️
...ervice-variables-tabs/use-service-variables-tab.ts	0.00%	11 Missing ⚠️
...-variables-tabs/service-variables-built-in-tab.tsx	0.00%	10 Missing ⚠️
.../associated-items-modal/associated-items-modal.tsx	71.42%	1 Missing and 7 partials ⚠️
...labels-annotations/settings-labels-annotations.tsx	0.00%	8 Missing ⚠️
.../service-variables-tabs/service-variables-utils.ts	28.57%	5 Missing ⚠️
...src/lib/variable-list/variable-list-action-bar.tsx	0.00%	2 Missing ⚠️
... and 5 more

Additional details and impacted files

@@                              Coverage Diff                               @@
##           feat/secrets-manager-service-creation-flow    #2721      +/-   ##
==============================================================================
- Coverage                                       45.50%   45.43%   -0.07%     
==============================================================================
  Files                                            1151     1125      -26     
  Lines                                           24578    24338     -240     
  Branches                                         7300     7229      -71     
==============================================================================
- Hits                                            11185    11059     -126     
+ Misses                                          11401    11338      -63     
+ Partials                                         1992     1941      -51     

Flag	Coverage Δ
unittests	45.43% <55.92%> (-0.07%)	⬇️

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