docs: document attendance scope for reverse event lookups

[shiyubi]

What improves for users?
The API Reference now documents the existing attendance filters for reverse event lookups by exhibitor ID, personnel ID, LinkedIn URL, and personnel name.

• Add attendance_scope enums, default value all, and invalid-value constraints.
• Explain visitor-only filtering: visitor excludes events with exhibitor or exhibitor-employee evidence.
• Include required lookup identifiers and attendance_scope in cURL examples and Try it.
• Add attendance_identity arrays to response schemas and examples.
• Align company-name event search documentation with visitor-only behavior.
• Synchronize OpenAPI copies and generated LLM documentation.
  Evidence and validation
  Documentation was checked against the existing client and service implementations. This PR contains documentation changes only; examples use placeholder identifiers and API keys.
  Validation completed after synchronizing with main:
• Public asset tests: 23 passed.
• Generated asset synchronization, JSON validation, and OpenAPI copy consistency: passed.
• git diff --check: passed.
• Redocly CLI 2.39.0: zero errors and warnings.
• Mintlify 4.2.740 build validation: passed.
• Four GET pages verified in local preview, including scope selection, required identifiers, cURL examples, and response identity arrays.
• I followed the target repository's contribution instructions.
• My factual claims have sources, and examples are clearly identified.
• I checked affected links and any repository-specific validation.
• I removed credentials, personal contact data, and private account information.