Tests: align reactive/marshes/reactive-runtime island names with live site

Update test-examples.sx to reference the real path-derived names
(~geography/<domain>/<stem>) instead of short aliases, drop the
alias chains in run_tests.ml, and add marshes/_islands loading so
the migrated one-per-file islands resolve. Fix the try-rerender-page
stub in boot-helpers.sx to accept the 3 args its callers pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/lib/boot-helpers.sx

@@ -806,7 +806,7 @@
     (define
       try-async-eval-content
       (fn (content-src env callback) (try-eval-content content-src env)))
-    (define try-rerender-page (fn () nil))
+    (define try-rerender-page (fn (page-name params result) nil))
     (define execute-action (fn () nil))
     (define bind-preload (fn () nil))
     (define persist-offline-data (fn () nil))