feat(examples): add saas tutorial skeleton

Add a compile-tested v1 tutorial skeleton that proves the production-shaped app boundary without provider-heavy scope: auth/session context, CSRF-checked mutation, local persistence adapter, generated form/slot/keyed row/page/push effects, plain CSS, SSE shape, and one explicit metrics island.

req: examples/001

req: auth/001

req: auth/002

req: auth/004

req: form/001

req: failure/004

req: page_swap/002

req: push/003

hemx-test/tests/examples_contract.rs

@@ -301,6 +301,8 @@ fn allowed_example_script(path: &Path, line: &str) -> bool {
     line.contains(r#"<script src="/hemx.js" defer></script>"#)
         || (path.ends_with("examples/techdemo/templates/app_shell.heml")
             && line.contains(r#"<script src="/island.js" defer></script>"#))
+        || (path.ends_with("examples/saas/templates/app_shell.heml")
+            && line.contains(r#"<script src="/metrics.js" defer></script>"#))
 }
 
 fn contains_inline_event_handler(line: &str) -> bool {