docs: simplify README and remove FreeBSD support

- Strip README to essentials with wiki references only
- Remove non-existent API docs and troubleshooting links
- Focus on quick start and actual integrations (merkwerk)
- Remove FreeBSD support from all installation scripts
- Clean up platform detection logic in scripts
- Maintain OpenBSD and Linux support only

Reduces maintenance burden and aligns with actual project scope.

install.sh

@@ -102,7 +102,7 @@ else
     echo ""
     echo "Next steps:"
     echo "1. Edit configuration file:"
-    if [ "$(uname)" = "OpenBSD" ] || [ "$(uname)" = "FreeBSD" ]; then
+    if [ "$(uname)" = "OpenBSD" ]; then
         echo "   /usr/local/etc/furt/furt.conf"
     else
         echo "   /etc/furt/furt.conf"