P0: Make clean installs free of demonstration data

[jusso-dev]

Goal

A normal Docker or homelab installation must be a real, empty Muster workspace. Synthetic incidents, users, alerts, messages, tasks, statistics, and agent runs exist only in explicit test/screenshot mode.

Scope

• Split installation bootstrap from screenshot/test seeding.
• Production boot runs migrations plus minimal bootstrap only.
• Bootstrap creates configured organisation, administrator actor, empty starter room(s), and usable agent definitions.
• Gate all synthetic UI fixtures behind explicit demo mode.
• Remove fake counts, unread badges, active runs, approvals, search results, integration statistics, and timeline records from clean mode.
• Keep screenshot generation deterministic with explicit demo mode.

Acceptance criteria

• Fresh-volume Docker install shows an empty usable workspace after login.
• No example employee, fake endpoint, incident, case, alert, or metric appears in clean mode.
• User can post a real message and create a real task.
• Production boot never runs demo seed.
• Screenshot/E2E fixtures work only with explicit demo mode.
• Automated test asserts clean operational-table state.

Verification

• Fresh-volume Docker smoke.
• Playwright clean-install test.
• Exact source scan for legacy/demo identities.
• Screenshot-mode regression.

[jusso-dev]

Implemented on main in 6fbe8b5. Added explicit clean bootstrap verification across 24 operational tables, demo-seed refusal unless MUSTER_DEMO_MODE=true, clean-install Chromium coverage for first message/task persistence, starter agent definitions, and CI ordering that proves clean state before demo seeding. Verified against fresh Docker volumes: health passed, clean DB assertion passed, clean Playwright passed, lint/typecheck/unit tests and Node 24 image build passed.