[TechNomadCode]

Adds a scenario tour to npm run dev:replay (slice 24): a panel in the page's corner that plays, step by step, every state the chat and the PRD can show, at the real model's pace, for free. The recorded answers alone never reach most of them, a table for one.

• 17 steps: two real recordings, then scripted answers for rich text, tables, folded and refused searches, a section with every kind of statement, a refused save, Open Questions, a long answer, a long wait for Stop, each kind of failure, the busy message and the used-up allocation.
• Scripted answers are written as recordings and played by the replay, so the searches, saves and quote checks run for real. A unit test holds every scripted quote to the interviews.
• The panel shows only when npm run dev:replay compiled the app (NEXT_PUBLIC_CHAT_REPLAY), never in a build for staging or production.

src/server and src/lib files, for the measurement lane: adds src/server/ai/scenarios.ts and src/lib/scenarios.ts, and changes src/server/ai/replay-chat-model.ts. All of them serve dev:replay only; nothing the real model receives changes, though the measurement's comparison will list them as code.

Checks, local: npm run verify (527 unit tests) and npm run test:e2e (69 tests, one new) passed.