Design local AI article studio

[shashmit]

What changed

• Adds the approved design specification for a laptop-local AI Article Studio.
• Defines the Next.js app, Bun worker, shared core package, MongoDB collections, and local Supermemory boundary.
• Specifies the eight-agent editorial workflow, OpenRouter/Gemini 3.5 Flash Lite configuration, private web-research evidence, review and approval states, recovery behavior, testing, and future publishing adapter.

Why

This creates an implementation-ready architecture for generating researched daily article drafts while keeping article data, approval, and semantic memory local.

User impact

There is no runtime behavior change yet. This PR establishes the reviewed design and acceptance criteria for the implementation phase.

Validation

• Reviewed repository placement against the existing monorepo.
• Reviewed standalone MongoDB durability, leasing, idempotency, and recovery constraints.
• Checked the specification for placeholders, contradictions, ambiguity, and whitespace errors.