add core view extension with JTE and Thymeleaf support

flash-extensions/flash-ext-view-thymeleaf/docs/model-and-globals.md

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+# Model and Globals
+
+`ViewModel` (from `flash-ext-view-core`) is the per-request model builder.
+
+## Merge Order
+
+Runtime merge order is:
+
+1. all extension globals under reserved `global` namespace
+2. local handler model
+
+Handlers cannot set top-level `global`; runtime throws fail-fast to prevent namespace collisions.
+
+## Globals
+
+Register globals on extension setup:
+
+```java
+new ThymeleafExtension()
+    .addGlobal("appName", req -> "Flash")
+    .addGlobal("path", req -> req.path());
+```
+
+Template usage:
+
+```html
+<span th:text="${global.appName}"></span>
+<span th:text="${global.path}"></span>
+```
+
+Keep globals cheap: no blocking I/O or heavy allocations.