chore: publish 4.0.0 #390

Why

General availability on latest (master plan Decision 1).

In scope

Publish, release notes, and the upgrade steps in the README.

Out of scope

Post-GA work.

Acceptance criteria

• npx @pacphi/agentic-kit@4.0.0 --version prints the version
• latest points at 4.0.0

Dependencies

Blocked by: #389, #384

Blocks: #391, #392, #393, #394, #409

Plan

• Release: 4.0.0
• Size: size:S · Workstream: ws:release
• Epic: chore: 4.0 release train (epic) #304
• Card: REL-GA in the card inventory
• Sources: Master plan (docs(plans): v4 GA master plan, supersession ledger and v5 registers #290) Decision 1

Verification

• npm view @pacphi/agentic-kit dist-tags