Send Algolia click events via search-insights

[zigzagdev]

Description

The Algolia dashboard's Analytics tab shows "No tracked searches" for Click-through Rate, Conversion Rate, and No Clicks Rate. No click tracking implementation (search-insights, clickAnalytics, queryID) exists anywhere in this codebase currently.

Without click events, there's no way to measure whether search results are actually useful to users (CTR, conversion, no-clicks rate), which makes it impossible to data-drive any future Algolia ranking/Rules tuning.

Changes needed (frontend)

• Add Algolia's official search-insights library.
• When a user clicks a search result, send a click event including: queryID (returned by the backend search API — see backend follow-up below), the result's Algolia objectID, and its position in the result list.
• Initialize search-insights with the same Algolia App ID / Search API key used for search.

Dependency

Backend needs to surface queryID and each hit's objectID in the /api/v1/heritages/search response first — tracked in zigzagdev/world-heritage-api#486.

Acceptance Criteria

• Clicking a search result sends a click event to Algolia Insights.
• Confirmed in the Algolia dashboard (Analytics tab) that Click-through Rate / No Clicks Rate start showing real data instead of "No tracked searches".