feat(core)!: introduce canonical authoring factories
Draft
ZR
1d ago+3222+3222+0123456789012345678901234567890123456789-3003-3003-0123456789012345678901234567890123456789
Breaking v3 authoring APIs: defineAgent, definePlanAgent, defineTool, defineWorkflow, and voltagent. Agent state lives in closures; planning agents compose extensions. Agent, PlanAgent, and VoltAgent are type-only exports.
Validated: 1,589 core tests, 76 scorer tests, builds, source and consumer types, package checks, lint, and formatting. Changeset includes a migration example.
Layer 1 of 4, targeting next. Explicit lifecycle, examples, and documentation follow.