Improve dev host handling and clarify backend port configuration (#532)

* fix: remove --host from npm run server command

Running `vite --host` exposes the dev server on all interfaces. However,
we should expose it on all interfaces only when `HOST` is set to `0.0.0.0`.
Otherwise, we should assume the user wants to bind to a host of their choice
and not expose the server on the network.

* fix: use src hostname for redirecting to Vite in development

Previously, the server redirected to Vite using `localhost` as the hostname.
Even if the user was using HOST="0.0.0.0", if they connected to server from
another device on the same network using `http://<host_ip>:3001`, the
server would redirect them to `http://localhost:5173`, which would not
work since `localhost` would resolve to the client's machine instead of the server.

* fix: use shared network hosts configuration for better proxy setup

- Normalize all localhost variants to 'localhost' for consistent proxy
configuration in Vite and server setup.
- use one source of truth for network hosts functions by moving them to
a shared
- log production and development urls

* refactor: rename PORT to SERVER_PORT for clarity

* chore: add comments explaining host normalization

* fix: add legacy PORT env fallback for server port configuration

* fix: add fallback for SERVER_PORT using PORT environment variable

---------

Co-authored-by: Haileyesus <something@gmail.com>
Co-authored-by: Simos Mikelatos <simosmik@gmail.com>

.env.example

@@ -17,7 +17,7 @@
 
 # Backend server port (Express API + WebSocket server)
 #API server
-PORT=3001
+SERVER_PORT=3001
 #Frontend port
 VITE_PORT=5173