feat(ext-web-bundler): add build-time asset scanning and static-frontend strategy

Introduces AssetDirectoryScanner, StaticFrontendStrategy, and WebBundlerBuild for
build-time asset discovery, plus config/docs updates for frontend-type resolution.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

flash-extensions/flash-ext-web-bundler/docs/build-time.md

@@ -0,0 +1,43 @@
+# Build-Time Manifest Generation
+
+`WebBundlerBuild` turns an already-built directory into the `asset-manifest.json` that
+`ClasspathAssetsSource` needs (see `asset-sources.md`). It does not run a frontend build itself —
+it only scans a directory that already contains the final files:
+
+- `VITE`: point it at whatever `dist/` the existing frontend build tooling already produces.
+- `STATIC`: point it directly at the static asset folder — there's no separate build step.
+
+It's meant to run once per build, from the consumer project's own build, not from the running
+application (`ClasspathAssetsSource` is explicitly unsupported in DEV — see `dev-lifecycle.md`).
+
+## Wiring it into a Maven build
+
+No dedicated Flash5 Maven plugin — `WebBundlerBuild` is a plain class with a `main`, invoked via
+the standard `exec-maven-plugin`, bound to run before the resources are packaged:
+
+```xml
+<plugin>
+    <groupId>org.codehaus.mojo</groupId>
+    <artifactId>exec-maven-plugin</artifactId>
+    <executions>
+        <execution>
+            <id>web-bundler-manifest</id>
+            <phase>process-classes</phase>
+            <goals><goal>java</goal></goals>
+            <configuration>
+                <mainClass>dev.relism.flash.ext.webbundler.WebBundlerBuild</mainClass>
+                <arguments>
+                    <argument>${project.build.outputDirectory}/web/dist</argument>
+                </arguments>
+            </configuration>
+        </execution>
+    </executions>
+</plugin>
+```
+
+This assumes the built frontend (`web/dist/`, or a static folder) is already copied under
+`target/classes/web/dist` by that point — e.g. via `maven-resources-plugin`'s `copy-resources`
+goal, or by running the frontend build with an output directory that points there directly. Once
+the manifest is written alongside those files, they're just classpath resources: a plain `mvn
+package` (or `maven-shade-plugin` for a fat jar) picks them up with no further configuration, and
+the app can then be configured with `.assetsFromClasspath("web/dist")`.