fix(api): support internal pusher host and normalize URL parsing (#6856)

[Mateidslx]

Fixes #6856

/claim #6856

Summary of Changes

In Kubernetes, Docker Compose, and ingress-managed deployments, the WebSocket endpoint accessed by client browsers (e.g. via a public reverse proxy like /websocket) typically diverges from the internal service address accessed by the backend (e.g. \keep-websocket-server:6001). Previously, configuring a relative path or host+path combination caused the backend to crash with
equests.exceptions.InvalidURL\ and frontend WebSockets to fail connecting.

This PR resolves this divergence cleanly with full backward compatibility:

1. Backend Dedicated Overrides (\keep/api/core/dependencies.py):

   • Supports \PUSHER_HOST_INTERNAL\ and \PUSHER_HOST_PRIVATE\ (with priority over \PUSHER_HOST).
   • Supports \PUSHER_PORT_INTERNAL\ and \PUSHER_PORT_PRIVATE.
   • Supports \PUSHER_USE_SSL_INTERNAL\ and \PUSHER_USE_SSL_PRIVATE.
   • Normalizes \pusher_host\ parsing to support full URLs (\http://..., \https://...), host:port pairs (\keep-websocket:6001), and host/path combinations (\soketi-svc/websocket).
   • Safely guards against relative paths (/websocket) without crashing, logging a clear actionable warning.

2. Frontend Support & Parsing (\keep-ui):

   • Supports \PUSHER_HOST_CLIENT\ and \PUSHER_HOST_PUBLIC\ (and port overrides) in \keep-ui/shared/lib/server/getConfig.ts.
   • Prevents \NaN\ port evaluation in \getConfig.ts\ when port is not explicitly specified.
   • Normalizes \wsHost, \wsPath, and \wsPort\ in \keep-ui/utils/hooks/usePusher.ts\ so that host+path and URL values cleanly separate into valid WebSocket host and path segments.

3. Documentation (\docs/deployment/configuration.mdx):

   • Documented the internal backend and client override environment variables.

4. Testing & Validation:

   • Added unit test suite in \ ests/test_pusher_dependencies.py\ covering all 11 resolution, override, and normalization permutations (disabled, relative path safety, internal/private overrides, host:port, http/https URLs, host/path, and numeric app ID validation).
   • Validated against repo linting rules using
     uff==0.11.4\ and \�lack.

[CLAassistant]

All committers have signed the CLA.

[Mateidslx]

Hi @shahargl, all CI checks are green, CLA is signed, and 11 unit tests in ests/test_pusher_dependencies.py cover all host/port/scheme override cases. Ready for review and merge!