docs: retire the deja-vu guide and ADR-0035 #322

Why

deja-vu leaves the kit (design Decision 4).

In scope

Move docs/deja-vu.md and ADR-0035 to docs/archive/; mark ADR-0035 superseded; remove deja-vu sections from the guides.

Out of scope

Code (#321).

Acceptance criteria

• No guide describes deja-vu as available
• Archive index rows exist

Dependencies

Blocked by: #321

Blocks: #385

Plan

• Release: 4.0.0-beta.1
• Size: size:S · Workstream: ws:project-scope
• Epic: feat: project-scope P0, removals and the enforcement baseline (epic) #295
• Card: P0-02 in the card inventory
• Sources: Design (docs(plans): project-scoped management design and its prerequisites #289) Removing deja-vu

Verification

• node scripts/run-tests.mjs focus tests/kit/docs-layout.test.mjs