Cache parsed components for 10x faster startup (2s → 200ms)

- Fix O(n²) postprocessing: compute_all_deps/io_refs/hash were called
  per-file (92x for sx app). Now deferred to single finalize_components()
  call after all files load.
- Add pickle cache in shared/sx/.cache/ keyed by file mtimes+sizes.
  Cache stores fully-processed Component/Island/Macro objects with deps,
  io_refs, and css_classes pre-computed. Closures stripped before pickle,
  rebuilt from global env after restore.
- Smart finalization: cached loads skip deps/io_refs recomputation
  (already in pickle), only recompute component hash.
- Fix ~sx-header → ~layouts/header ref in docs-content.sx

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

shared/infrastructure/factory.py

@@ -118,6 +118,11 @@ def create_base_app(
     setup_jinja(app)
     setup_sx_bridge(app)
     load_shared_components()
+    # Finalize shared components (deps, hash) now — service apps that call
+    # load_service_components() will re-finalize after loading their own.
+    from shared.sx.jinja_bridge import _rebuild_closures, _finalize_if_needed
+    _rebuild_closures()
+    _finalize_if_needed()
     load_relation_registry()
 
     # Load defquery/defaction definitions from {service}/queries.sx and actions.sx