Add search-selector template

[MicaPerdomo]

Summary

• Adds the search-selector template demonstrating the search selector pattern: a single script tool that dynamically routes queries to the correct retrieval based on topic parameters.
• Domain: Travel guide with 3 regions (Europe, Asia, Americas), 4 destinations per region = 12 Markdown docs.
• The SearchInformation script tool receives topic and question, looks up the matching Retrieval by name via Django ORM, executes the search, and aggregates results. Multi-topic search is supported via | separator (e.g., europe|asia).

What Is Included

• agents/tools.py — SearchInformation script tool (router)
• agents/searches.py — 3 BaseRetrievalTool subclasses (required for Cognitive API retrieval registration)
• agents/searchselector/ — Agent definition, scaffolds, system prompt
• data/ — 3 topics, 3 retrievals, formatter, ingestion config, 12 travel destination docs
• Updated templates/README.md and root README.md catalog entries

Test plan

• python manage.py makemigrations generates data + agents migrations
• python manage.py migrate data then migrate agents apply without errors
• python manage.py ingest europe/asia/americas ingests 12 docs (4 per topic)
• Single-region query: "What are the best things to do in Paris?" returns Europe results
• Multi-region query: "Tell me about street food in Bangkok and tacos in Mexico City" returns Asia + Americas results
• CI checks pass (README present, catalog entries updated)

[MicaPerdomo]

Superseded by #30 (search-selector example).