Unify scoped effects: scope as general primitive, provide as sugar

- Add `scope` special form to eval.sx: (scope name body...) or
  (scope name :value v body...) — general dynamic scope primitive
- `provide` becomes sugar: (provide name value body...) calls scope
- Rename provide-push!/provide-pop! to scope-push!/scope-pop! throughout
  all adapters (async, dom, html, sx) and platform implementations
- Update boundary.sx: Tier 5 now "Scoped effects" with scope-push!/
  scope-pop! as primary, provide-push!/provide-pop! as aliases
- Add scope form handling to async adapter and aser wire format
- Update sx-browser.js, sx_ref.py (bootstrapped output)
- Add scopes.sx docs page, update provide/spreads/demo docs
- Update nav-data, page-functions, docs page definitions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/test-aser.sx

@@ -301,3 +301,46 @@
   (deftest "spread in non-element context silently drops"
     (assert-equal "hello"
       (render-sx "(do (make-spread {:class \"card\"}) \"hello\")"))))
+
+
+;; --------------------------------------------------------------------------
+;; Scope tests — unified scope primitive
+;; --------------------------------------------------------------------------
+
+(defsuite "scope"
+
+  (deftest "scope with value and context"
+    (assert-equal "dark"
+      (render-sx "(scope \"sc-theme\" :value \"dark\" (context \"sc-theme\"))")))
+
+  (deftest "scope without value defaults to nil"
+    (assert-equal ""
+      (render-sx "(scope \"sc-nil\" (str (context \"sc-nil\")))")))
+
+  (deftest "scope with emit!/emitted"
+    (assert-equal "a,b"
+      (render-sx "(scope \"sc-emit\" (emit! \"sc-emit\" \"a\") (emit! \"sc-emit\" \"b\") (join \",\" (emitted \"sc-emit\")))")))
+
+  (deftest "provide is equivalent to scope with value"
+    (assert-equal "42"
+      (render-sx "(provide \"sc-prov\" 42 (str (context \"sc-prov\")))")))
+
+  (deftest "collect! works via scope (lazy root scope)"
+    (assert-equal "x,y"
+      (render-sx "(do (collect! \"sc-coll\" \"x\") (collect! \"sc-coll\" \"y\") (join \",\" (collected \"sc-coll\")))")))
+
+  (deftest "collect! deduplicates"
+    (assert-equal "a"
+      (render-sx "(do (collect! \"sc-dedup\" \"a\") (collect! \"sc-dedup\" \"a\") (join \",\" (collected \"sc-dedup\")))")))
+
+  (deftest "clear-collected! clears scope accumulator"
+    (assert-equal ""
+      (render-sx "(do (collect! \"sc-clear\" \"x\") (clear-collected! \"sc-clear\") (join \",\" (collected \"sc-clear\")))")))
+
+  (deftest "nested scope shadows outer"
+    (assert-equal "inner"
+      (render-sx "(scope \"sc-nest\" :value \"outer\" (scope \"sc-nest\" :value \"inner\" (context \"sc-nest\")))")))
+
+  (deftest "scope pops correctly after body"
+    (assert-equal "outer"
+      (render-sx "(scope \"sc-pop\" :value \"outer\" (scope \"sc-pop\" :value \"inner\" \"ignore\") (context \"sc-pop\"))"))))