Move version display to GET /api/health/version in HealthController

Uses GetApplicationVersion(Assembly.GetExecutingAssembly()) — the same
timestamp-based version already logged at startup and baked into the
assembly via the csproj <Version> property. Removes the minimal-API
/version endpoint from web/Program.cs and reverts the web Dockerfile
APP_VERSION build-arg (no longer needed).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/wwwroot/js/main.js

@@ -263,7 +263,7 @@
 
 	$('#year').text(new Date().getFullYear());
 
-	$.getJSON('/version').done(function (data) {
+	$.getJSON('/api/health/version').done(function (data) {
 		if (data && data.version) {
 			$('#app-version').text('v' + data.version);
 		}