fix: html-router modals and add insta snapshot tests.

Avoid nested forms in the scratchpad editor, centralize modal lifecycle in modal.js, return HTMX partials from archive, and add template compile plus layout snapshots.

html-router/src/routes/scratchpad/handlers.rs

@@ -385,8 +385,10 @@ pub async fn archive_scratchpad(
         .map(ScratchpadArchiveItem::from)
         .collect();
 
-    Ok(TemplateResponse::new_template(
+    // HTMX archive targets #main_section; return only the list partial, not full layout.
+    Ok(TemplateResponse::new_partial(
         "scratchpad/base.html",
+        "main",
         ScratchpadPageData {
             scratchpads: scratchpad_list,
             archived_scratchpads: archived_list,