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>

sx/sxc/pages/docs.sx

@@ -553,7 +553,9 @@
     :eval-source eval-source
     :parser-source parser-source
     :router-source router-source
-    :render-source render-source))
+    :render-source render-source
+    :deps-source deps-source
+    :engine-source engine-source))
 
 (defpage testing-page
   :path "/testing/<slug>"
@@ -570,6 +572,8 @@
     "parser" (run-modular-tests "parser")
     "router" (run-modular-tests "router")
     "render" (run-modular-tests "render")
+    "deps" (run-modular-tests "deps")
+    "engine" (run-modular-tests "engine")
     :else (dict))
   :content (case slug
     "eval" (~testing-spec-content
@@ -600,6 +604,20 @@
       :spec-source spec-source
       :framework-source framework-source
       :server-results server-results)
+    "deps" (~testing-spec-content
+      :spec-name "deps"
+      :spec-title "Dependency Analysis Tests"
+      :spec-desc "33 tests covering component dependency analysis — scan-refs, scan-components-from-source, transitive-deps, components-needed, scan-io-refs, and component-pure? classification."
+      :spec-source spec-source
+      :framework-source framework-source
+      :server-results server-results)
+    "engine" (~testing-spec-content
+      :spec-name "engine"
+      :spec-title "Engine Tests"
+      :spec-desc "37 tests covering engine pure functions — parse-time, parse-trigger-spec, default-trigger, parse-swap-spec, parse-retry-spec, next-retry-ms, and filter-params."
+      :spec-source spec-source
+      :framework-source framework-source
+      :server-results server-results)
     "runners" (~testing-runners-content)
     :else (~testing-overview-content
       :server-results server-results)))