[7a] Seed data + demo scenario

[andrmaz]

What to build

A seed script that populates a complete, repeatable demo scenario: one organization, two departments (e.g. Engineering and Product), a set of realistic documents per department, and active department policies that demonstrate policy enforcement. Running the seed produces a deterministic "wow moment" state ready for a stakeholder walkthrough.

Acceptance criteria

• pnpm seed (or equivalent) runs without errors and is idempotent.
• Seed creates org, departments, users, sources, indexed documents, and active policies.
• The demo path (login → MCP query → policy-enforced cited response → audit log) works end-to-end with seeded data.
• Seed is documented in the README with a short demo script.

Blocked by

• [6b] Audit log admin viewer #17 [6b] Audit log admin viewer