fix: correct summarizer typos and wire dead web search fallback route

[bhavyakeerthi3]

🐛Summary

Surgical hardening of the CrossDatabase agent: fixes pre-existing typos in the summarization prompt and resolves a silent "dead route" where web search decisions were never executed.

Changes

1. Prompt Improvements & Typo Fixes

src/agent/tasks/cross_database/summarize_reactome_uniprot.py

• Corrected typos in the expert curator system prompt (ADN → and, infromation → information)
• Fixed broken numbering sequence in the instruction list
• Updated prompt to support and prioritize external web search results when Reactome/UniProt data is insufficient

2. Wiring the Web Search Fallback

src/agent/profiles/cross_database.py

The Issue:
The perform_web_search route was hardcoded to point directly to generate_final_response — the agent would decide to search but skip execution entirely, producing incomplete responses.

The Fix:

• Added web_search_results to CrossDatabaseState
• Implemented perform_web_search node using the existing search_workflow
• Updated graph routing: assess_completeness → perform_web_search → generate_final_response

Impact

• Eliminates typos visible in final LLM responses
• Web search fallback now actually executes instead of being silently skipped
• Queries outside RAG coverage return real results instead of "I don't know"

Verification

• CrossDatabaseState correctly holds web_search_results
• Graph transition confirmed: assess_completeness → perform_web_search → generate_final_response
• tests/test_config.py passing

Fixes #123