feat: pass through SERVER_IGNORE_HIDDEN_FILES env

static-web-server skips dot-prefixed paths by default. Passing this
env through lets operators set SERVER_IGNORE_HIDDEN_FILES=false to
serve e.g. /.well-known/matrix/server for Matrix federation
delegation.

Backwards-compatible: unset means existing behaviour (hidden files
skipped).

.env.sample

@@ -9,6 +9,10 @@ LETS_ENCRYPT_ENV=production
 HTTP_SUBDIR=
 COMPOSE_FILE="compose.yml"
 
+## Serve dot-prefixed files/directories (e.g. /.well-known/).
+## Defaults to true (hidden). Set false to expose them.
+#SERVER_IGNORE_HIDDEN_FILES=false
+
 # Single Sign On via Traefik "file provider"
 #COMPOSE_FILE="$COMPOSE_FILE:compose.sso.yml"