fix(call-omo-agent): address cubic review findings and add requirement-based tests

- Fix agent-resolver.ts: add defensive validation on agent name (typeof, trim, filter)
- Fix tools.test.ts: correct mock to return {data: agents} matching SDK contract
- Fix agent-config-handler.ts: include opencode global/project agents in customAgentSummaries
- Add agent-resolver.test.ts: 14 requirement-based tests covering R1-R7 behavioral specs
- Add tools-edge-cases.test.ts: 5 integration tests for rollback, whitespace, dedup, session_id