fix(infra): expose Meilisearch via search.libnovel.cc for homelab runner indexing

- Add search.libnovel.cc Caddy vhost proxying to meilisearch:7700
- Pass MEILI_URL + MEILI_API_KEY from Doppler into homelab runner
- Set GODEBUG=preferIPv4=1 to work around missing IPv6 route on homelab
- Update comments to reflect runner now indexes books into Meilisearch

Caddyfile

@@ -30,6 +30,7 @@
 #   logs.libnovel.cc               → dozzle:8080   (Docker log viewer)
 #   uptime.libnovel.cc             → uptime-kuma:3001  (uptime monitoring)
 #   push.libnovel.cc               → gotify:80     (push notifications)
+#   search.libnovel.cc             → meilisearch:7700  (search index — homelab runner)
 #
 # Routes intentionally removed from direct-to-backend:
 #   /api/scrape/*                  — SvelteKit has /api/scrape/ counterparts
@@ -254,3 +255,12 @@ storage.libnovel.cc {
 	reverse_proxy minio:9000
 }
 
+# ── Meilisearch: exposed for homelab runner search indexing ──────────────────
+# The homelab runner connects here as MEILI_URL to index books after scraping.
+# Protected by MEILI_MASTER_KEY bearer token — Meilisearch enforces auth on
+# every request; Caddy just terminates TLS.
+search.libnovel.cc {
+	import security_headers
+	reverse_proxy meilisearch:7700
+}
+}