feat: System panels on the cache and places #372

Why

System shows global installs and a machine-wide process sweep (design: System).

In scope

Tool cache rows; runtime tagged by project and read-only; ak-cache and project state storage roots; reclaim advice; catalog surfaces; split the /api/system payload (B0.3).

Out of scope

Deleting anything.

Acceptance criteria

• /api/system is split and its response size measured before and after
• Runtime view writes nothing

Dependencies

Blocked by: #364, #339

Blocks: #388

Plan

• Release: 4.0.0-beta.4
• Size: size:M · Workstream: ws:project-scope
• Epic: feat: project-scope P6, the dashboard for all work (epic) #301
• Card: P6-10 in the card inventory
• Sources: Design (docs(plans): project-scoped management design and its prerequisites #289) System; v5 impact review (docs(plans): v4 GA master plan, supersession ledger and v5 registers #290) B0.3

Verification

• pnpm run test:ui