docs: add architecture documentation with workflow diagram

feat: log failed retry attempts at error level

docs: add disclaimer section to readme

feat: add ticker_resolver sub-agent for company name to ticker resolution

refactor: remove python-dotenv, use typed datetime result, add api key validation

feat: add retry logic with exponential backoff to agent

feat: add get_current_datetime tool and fix agent entry point

feat: add project scaffolding, source, tests, and tooling

initial commit