Fix SX client navigation: path-derived names, provide clash, component expansion

- inject_path_name: strip _islands/ convention dirs from path-derived names
- page-functions.sx: fix geography (→ ~geography) and isomorphism (→ ~etc/plan/isomorphic)
- request-handler.sx: rewrite sx-eval-page to call page functions explicitly
  via env-get+apply, avoiding provide special form intercepting (provide) calls
- sx_server.ml: set expand-components? on AJAX aser paths so server-side
  components expand for the browser (islands stay unexpanded for hydration)
- Rename 19 component references in geography/spreads, geography/provide,
  geography/scopes to use path-qualified names matching inject_path_name output

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sx/sx/page-functions.sx

@@ -24,9 +24,7 @@
 
 (define
   geography
-  (fn
-    (content)
-    (if (nil? content) (quote (~geography/index-content)) content)))
+  (fn (content) (if (nil? content) (quote (~geography)) content)))
 
 (define
   applications
@@ -104,7 +102,7 @@
     (slug)
     (if
       (nil? slug)
-      (quote (~geography/isomorphism))
+      (quote (~etc/plan/isomorphic))
       (case
         slug
         "bundle-analyzer"