Fix PWA installability and update contributor docs links

[EstevesAndre]

Summary

This PR restores working PWA behavior and fixes stale contributor documentation links.

Target branch: development
Source branch: fix/pwa-service-worker-scope

Problem

PWA support was present in changelog/release notes, but installability/runtime behavior was broken in practice.
Contributor docs also had outdated links and an incomplete local dependency step.

Root Causes

• Service worker registration used js/sw.js (scope under /js/ instead of /)
• webui/js/sw.js was empty, so no real SW behavior existed
• Manifest/app metadata needed stronger installability wiring
• Documentation had stale references (development.md, websocket-infrastructure.md)
• Local dev setup instructions missed requirements2.txt (needed for override pins used in Docker)

Changes

PWA fixes

• Added a real root service worker: webui/sw.js
• Kept compatibility shim: webui/js/sw.js imports /sw.js
• Registered service worker with root scope in app shell
• Switched manifest reference to absolute path
• Added/installability metadata in HTML/manifest
• Added PNG app icons and Apple touch icon:
  • webui/public/icon-192.png
  • webui/public/icon-512.png
  • webui/public/apple-touch-icon.png
• Updated webui/js/manifest.json with id, scope, and PNG icons

Docs fixes

• Fixed stale links in:
  • docs/guides/contribution.md
  • docs/developer/architecture.md
  • docs/setup/dev-setup.md
• Updated local setup instructions to include:
  • pip install -r requirements2.txt
    so local development matches Docker dependency behavior.

Validation

• Added/ran focused regression test:
  • python3 -m pytest tests/test_pwa_wiring.py
• Confirmed PWA wiring expectations in app/login/manifest and service worker files.

Notes

This PR fixes repo-side PWA and docs issues.
Live installability on VPS still depends on secure origin/browser policy (https:// or localhost).