Refactor environment variables with shorter names and add comprehensive override support

- Rename OVERRIDE_INTERFACE_* to WG_* (shorter, non-conflicting)
- Add interface overrides: WG_PORT, WG_DEVICE, WG_MTU, WG_IPV4_CIDR, WG_IPV6_CIDR, WG_ENABLED
- Add client config overrides: WG_HOST, WG_CLIENT_PORT, WG_DEFAULT_DNS, WG_DEFAULT_ALLOWED_IPS, WG_DEFAULT_MTU, WG_DEFAULT_PERSISTENT_KEEPALIVE
- Add general config overrides: WG_SESSION_TIMEOUT, WG_METRICS_PROMETHEUS, WG_METRICS_JSON
- Update all API endpoints to apply and filter overrides
- Update documentation with all new environment variables
- Exclude AmneziaWG parameters (j*, s*, i*, h*) as requested

Co-authored-by: kaaax0815 <32197462+kaaax0815@users.noreply.github.com>

src/server/utils/WireGuard.ts

@@ -154,6 +154,7 @@ class WireGuard {
     const wgInterface = await Database.interfaces.get();
     const wgInterfaceWithOverrides = applyInterfaceOverrides(wgInterface);
     const userConfig = await Database.userConfigs.get();
+    const userConfigWithOverrides = applyUserConfigOverrides(userConfig);
 
     const client = await Database.clients.get(clientId);
 
@@ -163,7 +164,7 @@ class WireGuard {
 
     return wg.generateClientConfig(
       wgInterfaceWithOverrides,
-      userConfig,
+      userConfigWithOverrides,
       client,
       {
         enableIpv6: !WG_ENV.DISABLE_IPV6,