Enhance iSamples Explorer with faceted search and bookmarkable URLs

- Add text search across label, description, and place name
- Replace source dropdown with checkbox filters showing dynamic counts
- Add view mode toggle: Globe / List / Table
- Add URL state sync for bookmarkable searches (?q=pottery&sources=OPENCONTEXT)
- Auto-load data when filters change (remove manual Load button)
- Promote Interactive Explorer to top-level sidebar navigation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: rdhyee

_quarto.yml

@@ -43,6 +43,9 @@ website:
         - icon: github
           text: Github repositories
           href: "https://github.com/isamplesorg/"
+      - text: "Interactive Explorer"
+        href: tutorials/isamples_explorer.qmd
+        aria-label: "Search and explore 6.7M samples"
       - section: "Getting Started"
         contents:
         - text: "iSamples Tutorials Overview"