feat: the single legacy check #336

Why

The new version carries no migration code (design Decision 7).

In scope

Detect kit.json, ~/.local/state/agentic-kit or a user-scope claude-flow entry; init and sync stop and print the three steps; status and the dashboard show one Older installation row.

Out of scope

Migration.

Acceptance criteria

• Each of the three signals triggers the stop
• No other legacy logic exists

Dependencies

Blocked by: #330

Blocks: #338, #385

Plan

• Release: 4.0.0-beta.1
• Size: size:S · Workstream: ws:project-scope
• Epic: feat: project-scope P1, project layout and ak init (epic) #296
• Card: P1-07 in the card inventory
• Sources: Design (docs(plans): project-scoped management design and its prerequisites #289) The new version's single check

Verification

• node scripts/run-tests.mjs focus (new legacy check tests)