feat: add Cypress e2e tests for dashboard push actions

[fabiovincenzi]

Fixes #1390

• Add Cypress e2e tests for the admin UI dashboard's push management flows (approve, reject, cancel)
• Fix disabled prop not being forwarded in CustomButton component, which prevented the attestation confirm button from being properly disabled
• Add data-testid attributes to push detail action buttons and attestation dialog for reliable test selectors
• Organise Cypress tests into cypress/e2e/ (local) and cypress/e2e/docker/ (require Docker); local tests continue to run in the Node/MongoDB matrix in ci.yml, Docker tests run in e2e.yml
• Add cypress:run:docker script targeting Docker-only tests
• Add Cypress Docker step to e2e.yml alongside existing vitest e2e tests, with log dump and screenshot upload on failure
• Make existing Cypress tests (repo.cy.js) compatible with Docker environment by replacing hardcoded URLs with Cypress.env('API_BASE_URL')
• Pass git credentials via GIT_CONFIG_* env vars in createPush to avoid exposing them in CI logs

[netlify]

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🔨 Latest commit	e36872a
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.37%. Comparing base (468bd12) to head (e36872a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1403   +/-   ##
=======================================
  Coverage   81.37%   81.37%           
=======================================
  Files          67       67           
  Lines        4735     4735           
  Branches      819      819           
=======================================
  Hits         3853     3853           
  Misses        867      867           
  Partials       15       15           

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