KNOX-3234: Upgrade Admin UI Angular to 21+, bootstrap to 5+

[hanicz]

KNOX-3234 - Upgrade Admin UI libraries/frameworks

What changes were proposed in this pull request?

Summary

Upgrades the Knox Admin UI from Angular 13 to Angular 21 and Bootstrap 3 to Bootstrap 5, along with a full modernization of the frontend architecture.

Framework upgrades

• Angular: 13 → 21 (standalone components, new control flow syntax @if/@for, removed NgModules)
• Bootstrap: 3.4 → 5.3
• Angular Material/CDK: added for table/paginator components (green-themed)
• SweetAlert2: 11.6 → 11.26 (ESM import)
• js-yaml: 3 → 4 (ESM import, removed deprecated safeLoad/safeDump)

Architecture changes

• Migrated from app.module.ts (NgModule) to standalone component architecture
• Reorganized file structure: models into model/, services into service/, components into dedicated directories
• Replaced .eslintrc.json with flat eslint.config.js
• Removed all .spec.ts boilerplate files (no tests were implemented)
• Created reusable ModalComponent utility (replaces Bootstrap JS modals)

UI/Styling overhaul

• New styles.scss with a consistent green theme palette ($primary: #4caf50)
• Custom-styled panels, buttons, inputs, selects, checkboxes, and validation messages
• Green-themed .btn-primary, form focus states, and accent-color for checkboxes
• Material Icons integration with contextual coloring (add=green, remove→red on hover, etc.)
• Replaced inline style="color: red" validation with .validation-error styled badges
• Responsive resource list with mat-table and mat-paginator

Cleanup

• Removed unused model files (rewrite-rule.ts, rewrite-rules.ts), dead methods, unused properties, and commented-out code blocks
• Removed legacy files: styles.css, sticky-footer.css, typings.d.ts, index.ts, app/main.ts

How was this patch tested?

Tested locally

Integration Tests

N/A

UI changes

[github-actions]

Test Results

22 tests   22 ✅  1s ⏱️
 1 suites   0 💤
 1 files     0 ❌

Results for commit 4702bd1.

[smolnar82]

As discussed offline, the changes and the upgrade looks good. I only want to request one change: make the editor scrollable.