Phase 3: Client-side routing with SX page registry + routing analyzer demo

Add client-side route matching so pure pages (no IO deps) can render
instantly without a server roundtrip. Page metadata serialized as SX
dict literals (not JSON) in <script type="text/sx-pages"> blocks.

- New router.sx spec: route pattern parsing and matching (6 pure functions)
- boot.sx: process page registry using SX parser at startup
- orchestration.sx: intercept boost links for client routing with
  try-first/fallback — client attempts local eval, falls back to server
- helpers.py: _build_pages_sx() serializes defpage metadata as SX
- Routing analyzer demo page showing per-page client/server classification
- 32 tests for Phase 2 IO detection (scan_io_refs, transitive_io_refs,
  compute_all_io_refs, component_pure?) + fallback/ref parity
- 37 tests for Phase 3 router functions + page registry serialization
- Fix bootstrap_py.py _emit_let cell variable initialization bug
- Fix missing primitive aliases (split, length, merge) in bootstrap_py.py

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

sx/sxc/pages/docs.sx

@@ -416,6 +416,9 @@
     "bundle-analyzer" (~bundle-analyzer-content
       :pages pages :total-components total-components :total-macros total-macros
       :pure-count pure-count :io-count io-count)
+    "routing-analyzer" (~routing-analyzer-content
+      :pages pages :total-pages total-pages :client-count client-count
+      :server-count server-count :registry-sample registry-sample)
     :else (~plan-isomorphic-content)))
 
 (defpage bundle-analyzer
@@ -432,6 +435,20 @@
     :pages pages :total-components total-components :total-macros total-macros
     :pure-count pure-count :io-count io-count))
 
+(defpage routing-analyzer
+  :path "/isomorphism/routing-analyzer"
+  :auth :public
+  :layout (:sx-section
+    :section "Isomorphism"
+    :sub-label "Isomorphism"
+    :sub-href "/isomorphism/"
+    :sub-nav (~section-nav :items isomorphism-nav-items :current "Routing Analyzer")
+    :selected "Routing Analyzer")
+  :data (routing-analyzer-data)
+  :content (~routing-analyzer-content
+    :pages pages :total-pages total-pages :client-count client-count
+    :server-count server-count :registry-sample registry-sample))
+
 ;; ---------------------------------------------------------------------------
 ;; Plans section
 ;; ---------------------------------------------------------------------------