refactor(techdemo): compose page with hemplate views

Move the techdemo page shell and remaining board/inspector/hero boundaries to hemplate-owned views instead of Rust raw HTML or placeholder replacement. Keep rendered HTML assertions DOM-aware with scraper.

req: html_safety/002

req: view/001

req: test/005

slhx-core/src/lib.rs

@@ -143,6 +143,18 @@ impl SafeHtml {
     }
 }
 
+impl AsRef<str> for SafeHtml {
+    fn as_ref(&self) -> &str {
+        self.as_str()
+    }
+}
+
+impl core::fmt::Display for SafeHtml {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
 /// A generated, checked CSS class token.
 ///
 /// Plain CSS/SCSS owns appearance; slhx only gives Rust a typed reference to