fix: CORS error and restore PWA manifest functionality respecting auth redirects for subpath deployments.

[pantierra]

Currently I get an error like this:

https://eoapi.develop.eoepca.org/manager/meta/manifest.webmanifest' 
from origin 'https://eoapi.develop.eoepca.org' has been blocked by CORS policy: 
Cross origin requests are only supported for protocol schemes: chrome, 
chrome-extension, chrome-untrusted, data, http, https, isolated-app.

This PR attempt to fix this CORS error and PWA manifest functionality for subpath deployments by changing how PUBLIC_URL is handled:

• Build time: Use / as PUBLIC_URL and convert hardcoded paths to runtime placeholders
• Runtime: Replace placeholders with actual deployment path via docker-entrypoint.sh
• Auth redirects: Added getBasePath() and getRedirectUri() utilities to properly handle Keycloak redirects for subpath deployments

This ensures manifest files, assets, and authentication work correctly whether deployed at root (/) or a subpath (/manager/).