fix: maintain Services dropdown header from one canonical source

The site header / Services mega-dropdown was duplicated across two render
systems (Astro pages via Base.astro->nav.html, and ~80 pre-rendered static
public/**/index.html pages each embedding their own copy). They had drifted
into 5 different variants (missing 'New Carrier Setup', misplaced Healthcare
column, NEW vs FREE badges, em-dash encoding differences), so
dev.performancewest.net, the order pages, and the rest of the site disagreed.

- Make site/src/partials/nav.html the single source of truth (adopts the most
  complete variant).
- Add scripts/sync_nav.py to rewrite every static page's <nav> block from
  nav.html (idempotent; --check guards against drift in CI/deploy).
- Run the sync automatically in deploy.sh and scripts/deploy-dev.sh.
- Deprecate scripts/inject_healthcare_nav.py (now delegates to sync_nav.py).
- Neutralize the broken no-op SiteNav.astro component.

All 80 headers + the Astro-built order pages now render the identical dropdown.

site/src/components/SiteNav.astro

@@ -1,6 +1,13 @@
 ---
-// Production site navigation — extracted from the static homepage.
-// This component is included in Base.astro to give all Astro-built
-// pages the same nav as the static pages in public/.
+// DEPRECATED / unused.
+//
+// Site navigation is rendered from a single canonical source:
+//   - Astro pages: layouts/Base.astro reads src/partials/nav.html and injects it.
+//   - Static pages (public/**/index.html): kept byte-identical to nav.html by
+//     scripts/sync_nav.py (run on every deploy).
+//
+// This component used to attempt an Astro.glob() include but was a no-op
+// (it always rendered an empty string). It is intentionally left empty so
+// any stray imports keep compiling; do NOT add nav markup here -- edit
+// src/partials/nav.html instead.
 ---
-<Fragment set:html={await Astro.glob('../partials/nav.html').then(() => '').catch(() => '')} />