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.

scripts/deploy-dev.sh

@@ -10,6 +10,16 @@
 
 set -euo pipefail
 
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+# Single source of truth for the header: rewrite every static page's <nav>
+# block from site/src/partials/nav.html so the Services dropdown can never
+# drift between dev.performancewest.net, the order pages, and the rest of
+# the site. Idempotent.
+echo "=== Syncing canonical site header (Services dropdown) ==="
+python3 "$SCRIPT_DIR/sync_nav.py"
+
 REMOTE="deploy@207.174.124.71"
 SSH="ssh -p 22022"
 SCP="scp -P 22022"