Add STATIC environment variable for browser-only deployment mode

Implement STATIC=1 environment variable to enable browser-only deployment
without proxy server infrastructure. Uses WS4KP_SERVER_AVAILABLE flag to
distinguish between server-backed and static deployments for proper URL
rewriting and User-Agent header handling.

- Add STATIC env var to skip proxy route registration at startup
- Inject WS4KP_SERVER_AVAILABLE flag via EJS template based on STATIC mode
- Update fetch.mjs to conditionally send User-Agent headers based on server availability
- Update url-rewrite.mjs to skip proxy rewriting when server is unavailable
- Use renderIndex helper for consistent template data across dev/prod modes
- Improve music playlist logging

Benefits of integrated approach:
- Single environment variable controls both server and client behavior
- Flag injection happens once at render time, not on every request
- No runtime HTML string manipulation overhead
- Clean separation between server-backed and static deployment logic
- Same codebase supports both deployment modes without duplication

Static mode (STATIC=1): Direct API calls to external services, no caching
Server mode (default): Local proxy with caching and API request observability

server/scripts/modules/utils/url-rewrite.mjs

@@ -8,6 +8,10 @@ const rewriteUrl = (_url) => {
 	// Handle both string URLs and URL objects
 	const url = typeof _url === 'string' ? new URL(_url) : new URL(_url.toString());
 
+	if (!window.WS4KP_SERVER_AVAILABLE) {
+		return url;
+	}
+
 	// Rewrite the origin to use local proxy server
 	if (url.origin === 'https://api.weather.gov') {
 		url.protocol = window.location.protocol;