Add deps and engine test specs, bootstrap engine to Python

New test specs (test-deps.sx: 33 tests, test-engine.sx: 37 tests) covering
component dependency analysis and engine pure functions. All 6 spec modules
now have formal SX tests: eval (81), parser (39), router (18), render (23),
deps (33), engine (37) = 231 total.

- Add engine as spec module in bootstrap_py.py (alongside deps)
- Add primitive aliases (trim, replace, parse_int, upper) for engine functions
- Fix parse-int to match JS parseInt semantics (strip trailing non-digits)
- Regenerate sx_ref.py with --spec-modules deps,engine
- Update all three test runners (run.js, run.py, sx-test-runner.js)
- Add Dependencies and Engine nav items and testing page entries
- Wire deps-source/engine-source through testing overview UI

Node.js: 231/231 pass. Python: 226/231 (5 pre-existing parser/router gaps).

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

shared/static/scripts/sx-test-runner.js

@@ -131,6 +131,35 @@
     }
   }
 
+  function loadDepsFromBootstrap(env) {
+    if (Sx.scanRefs) {
+      env["scan-refs"] = Sx.scanRefs;
+      env["scan-components-from-source"] = Sx.scanComponentsFromSource;
+      env["transitive-deps"] = Sx.transitiveDeps;
+      env["compute-all-deps"] = Sx.computeAllDeps;
+      env["components-needed"] = Sx.componentsNeeded;
+      env["page-component-bundle"] = Sx.pageComponentBundle;
+      env["page-css-classes"] = Sx.pageCssClasses;
+      env["scan-io-refs"] = Sx.scanIoRefs;
+      env["transitive-io-refs"] = Sx.transitiveIoRefs;
+      env["compute-all-io-refs"] = Sx.computeAllIoRefs;
+      env["component-pure?"] = Sx.componentPure_p;
+      env["test-env"] = function() { return env; };
+    }
+  }
+
+  function loadEngineFromBootstrap(env) {
+    if (Sx.parseTime) {
+      env["parse-time"] = Sx.parseTime;
+      env["parse-trigger-spec"] = Sx.parseTriggerSpec;
+      env["default-trigger"] = Sx.defaultTrigger;
+      env["parse-swap-spec"] = Sx.parseSwapSpec;
+      env["parse-retry-spec"] = Sx.parseRetrySpec;
+      env["next-retry-ms"] = function(cur, cap) { return Math.min(cur * 2, cap); };
+      env["filter-params"] = Sx.filterParams;
+    }
+  }
+
   // --- Legacy runner (monolithic test.sx) ---
   window.sxRunTests = function(srcId, outId, btnId) {
     var src = document.getElementById(srcId).textContent;
@@ -169,6 +198,8 @@
     "parser": { needs: ["sx-parse"] },
     "router": { needs: [] },
     "render": { needs: ["render-html"] },
+    "deps":   { needs: [] },
+    "engine": { needs: [] },
   };
 
   window.sxRunModularTests = function(specName, outId, btnId) {
@@ -190,8 +221,10 @@
         var sn = specs[si];
         if (!SPECS[sn]) continue;
 
-        // Load router from bootstrap if needed
+        // Load module functions from bootstrap
         if (sn === "router") loadRouterFromBootstrap(ctx.env);
+        if (sn === "deps") loadDepsFromBootstrap(ctx.env);
+        if (sn === "engine") loadEngineFromBootstrap(ctx.env);
 
         // Find spec source — either per-spec textarea or embedded in overview
         var specEl = document.getElementById("test-spec-" + sn);