Spec explorer data endpoint, spec file finder, browser render test (failing)

- Add spec-explorer-data-by-slug helper with _SPEC_SLUG_MAP
- _find_spec_file searches spec/, web/, shared/sx/ref/ directories
- defpage specs-explore-page uses :data for server-side data fetch
- test_evaluator_renders_in_browser: failing test for client-side rendering
  (client re-evaluates defpage content, find-spec unavailable — pre-existing)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/projects/-root-rose-ash/memory/feedback_sx_navigation.md

@@ -0,0 +1,17 @@
+---
+name: SX navigation single-source-of-truth
+description: Navigation must be defined once in nav-data.sx — no fragment URLs, no duplicated case statements, use make-page-fn for convention-based routing
+type: feedback
+---
+
+Never use fragment URLs (#anchors) in the SX docs nav system. Every navigable item must have its own Lisp URL.
+
+**Why:** Fragment URLs don't work with the SX URL routing system — fragments are client-side only and never reach the server, so nav resolution can't identify the current page.
+
+**How to apply:**
+- `nav-data.sx` is the single source of truth for all navigation labels, hrefs, summaries, and hierarchy
+- `page-functions.sx` uses `make-page-fn` (convention-based) or `slug->component` to derive component names from slugs — no hand-written case statements for simple pages
+- Overview/index pages should generate link lists from nav-data variables (e.g. `reactive-examples-nav-items`) rather than hardcoding URLs
+- To add a new simple page: add nav item to nav-data.sx, create the component file. That's it — the naming convention handles routing.
+- Pages that need server-side data fetching (reference, spec, test, bootstrapper, isomorphism) still use custom functions with explicit case clauses
+- Legacy Python nav lists in `content/pages.py` have been removed — nav-data.sx is canonical