feat(api): add BaseAgentConfig, AgencyOptions, and extended result types

Introduces src/api/types.ts with the full Agency API type surface:
SecurityTier, MemoryType, AgencyStrategy, BaseAgentConfig, AgencyOptions,
AgencyStreamPart discriminated union, AgencyTraceEvent, AgentCallRecord,
ApprovalRequest/Decision, all sub-config interfaces, AgencyCallbacks,
CompiledStrategy, Agent/Agency interfaces, and AgencyConfigError.

Extends GenerateTextResult with agentCalls, trace, and parsed fields.
Adds 47-test suite in agency-types.test.ts covering class behaviour,
discriminated-union narrowing, literal unions, and structural shapes.

Author: jddunn