[KanishJebaMathewM]

Description

Stored authentication sessions are now validated during startup, with invalid or timed-out sessions cleared safely. This also adds real backend account deletion with API error handling and removes the unsupported subscription cancellation action that previously showed success without performing a cancellation.

Type of Change

• fix: Bug fix (non-breaking change which fixes an issue)
• feat: New feature (non-breaking change which adds functionality)
• refactor: Code refactor (no functional changes, no API changes)
• docs: Documentation update
• test: Adding or updating tests
• chore: Maintenance (CI, dependencies, tooling)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Screenshots / Recordings

Not applicable.

Checklist

• I have linked the related issue above.
• My code follows the coding standards of this project.
• I have added tests that prove my fix is effective or my feature works.
• New and existing tests pass locally (npm run unit and npm run test).
  • 47 focused authentication and account tests pass.
  • ESLint and the production build pass.
• My changes generate no new lint warnings or errors (npm run lint).
• My PR title follows Conventional Commits (e.g., fix: resolve login redirect).