Preserve event filter index seeks

[brainx]

Summary

• restore indexed event filtering after the fixed-query Bandit remediation by selecting one of six immutable SQL variants
• retain direct primary-key cursor seeks and direct indexed predicates for run_id, plan_id, node_id, and event_type
• keep every external filter value parameterized while preserving combined filtering, ascending ordering, limits, and cursor behavior
• add a query-plan regression for the run_id index alongside the existing cursor-plan coverage

Scope

This is a focused follow-up to #2 discovered during the final merge audit. It changes only the event query implementation and its focused tests; Zeus compatibility, OpenAPI fixtures, Kimi support, versions, and documentation are unchanged.

Verification

• .venv/bin/python -m unittest tests.test_events — 6 tests passed
• sh scripts/repo_check.sh — passed; 201 tests, 85% coverage, formatting, Ruff, mypy, Bandit, lifecycle smoke, and repository scans
• sh scripts/wheel_smoke.sh — sdist and wheel built successfully; both passed package checks
• .venv/bin/bandit -r olymp — no issues identified; zero skipped lines and zero suppressions
• query-plan regressions — cursor uses SEARCH events USING INTEGER PRIMARY KEY; run_id uses SEARCH events USING INDEX idx_events_run_id
• git diff --check — passed