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/sx/ref/bootstrap_py.py

@@ -854,6 +854,7 @@ ADAPTER_FILES = {
 SPEC_MODULES = {
     "deps": ("deps.sx", "deps (component dependency analysis)"),
     "router": ("router.sx", "router (client-side route matching)"),
+    "engine": ("engine.sx", "engine (fetch/swap/trigger pure logic)"),
 }
 
 
@@ -958,7 +959,7 @@ def compile_ref_to_py(
                     Valid names: continuations.
                     None = no extensions.
         spec_modules: List of spec module names to include.
-                      Valid names: deps.
+                      Valid names: deps, engine.
                       None = no spec modules.
     """
     # Determine which primitive modules to include
@@ -1832,10 +1833,15 @@ PRIMITIVES["parse-int"] = lambda v, d=0: _sx_parse_int(v, d)
 PRIMITIVES["parse-datetime"] = lambda s: str(s) if s else NIL
 
 def _sx_parse_int(v, default=0):
-    try:
-        return _b_int(v)
-    except (ValueError, TypeError):
+    if v is None or v is NIL:
         return default
+    s = str(v).strip()
+    # Match JS parseInt: extract leading integer portion
+    import re as _re
+    m = _re.match(r'^[+-]?\\d+', s)
+    if m:
+        return _b_int(m.group())
+    return default
 ''',
 
     "stdlib.text": '''
@@ -1976,6 +1982,10 @@ concat = PRIMITIVES["concat"]
 split = PRIMITIVES["split"]
 length = PRIMITIVES["len"]
 merge = PRIMITIVES["merge"]
+trim = PRIMITIVES["trim"]
+replace = PRIMITIVES["replace"]
+parse_int = PRIMITIVES["parse-int"]
+upper = PRIMITIVES["upper"]
 '''
 
 
@@ -2189,7 +2199,7 @@ def main():
     parser.add_argument(
         "--spec-modules",
         default=None,
-        help="Comma-separated spec modules (deps). Default: none.",
+        help="Comma-separated spec modules (deps,engine). Default: none.",
     )
     args = parser.parse_args()
     adapters = args.adapters.split(",") if args.adapters else None