Add web_search parameter to run_meeting()

[sammargolis]

Summary

• Adds a web_search: bool = False parameter to run_meeting() that enables OpenAI's built-in web search for agents during meetings
• Uses the web_search_options top-level parameter on client.chat.completions.create() (the correct Chat Completions API surface — not a tools list entry)
• Both create() call sites are updated so web search persists through PubMed tool-call follow-up turns

Changes

• src/virtual_lab/run_meeting.py — new parameter, import, and both API call sites
• tests/test_run_meeting.py — 5 new tests (first tests in the repo)
• README.md — documents both pubmed_search and web_search parameters

Usage

run_meeting(
    meeting_type="individual",
    agenda="...",
    team_member=agent,
    web_search=True,  # enables OpenAI web search
)

Test Plan

• pytest tests/test_run_meeting.py -v — 5 tests pass
• web_search=False passes NOT_GIVEN to the API (no regression)
• web_search=True passes WebSearchOptions() to both create() call sites
• web_search=True + pubmed_search=True work together without conflict

Closes #17