add core view extension with JTE and Thymeleaf support

flash/src/main/java/dev/relism/Flash.java

@@ -10,7 +10,7 @@ package dev.relism;
  * <p>Dev mode enables:
  * <ul>
  *   <li>HTML error pages with full stack traces (default: JSON generic responses in prod)</li>
- *   <li>Template cache disabled in {@code flash-ext-view}</li>
+ *   <li>Template cache disabled in {@code flash-ext-view-thymeleaf}</li>
  * </ul>
  *
  * <p>Extensions can read {@link #DEV} to branch behavior without re-implementing the detection:

flash/src/main/java/dev/relism/extension/FlashScope.java

@@ -31,7 +31,7 @@ public final class FlashScope extends FlashRegistrar<FlashScope> {
     private final List<RouteDefinition> deferredRoutes   = new ArrayList<>();
 
     FlashScope(String namespace, FlashContext parentCtx) {
-        this.namespace = namespace;
+        this.namespace = PathUtils.sanitize(namespace);
         this.ctx       = parentCtx.child();
     }
 
@@ -54,5 +54,5 @@ public final class FlashScope extends FlashRegistrar<FlashScope> {
 
     List<RouteDefinition> routes() { return deferredRoutes; }
 
-    private String ns(String path) { return namespace + PathUtils.sanitize(path); }
+    private String ns(String path) { return PathUtils.join(namespace, path); }
 }