Upgrade AxeOS to Angular 19

[mutatrum]

This is an experimental migration to Angular 19. One of the biggest changes is that it's based off a default theme, instead of a copy-drop into the project. Not all elements are styled the same, so it needs polish, but this is mainly a feasibility exercise, and probably needs to be done again after #1622 and maybe other pending PRs.

The line count of this PR is massive, however, if you break it down:

• package-lock.json: +8,900/-7,800
• base theme files: 0/-7,659 (97 files deleted, 450KB!)
• Actual changes: +377/-283

Rationale was the increasing number of security issues in the npm build part, which for a large part were coming from the Angular 18 dependencies:

Before: 60 vulnerabilities (9 low, 11 moderate, 39 high, 1 critical)
After: 8 vulnerabilities (1 moderate, 7 high)

Following this, the next step would be to migrate from PrimeFlex to Tailwind. But that can be done gradually.

Prior art: #885

[github-actions]

Test Results

 2 files  ±0   2 suites  ±0   0s ⏱️ ±0s
83 tests ±0  83 ✅ ±0  0 💤 ±0  0 ❌ ±0 
85 runs  ±0  85 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit e9a8e5b. ± Comparison against base commit bba9e6a.

♻️ This comment has been updated with latest results.