docs: align tracked files to single coherent SoT

Contradictions resolved:

- AGENTS.md: add 'Known stale PRD lines' section (FR17, FR19, FR40, NFR, FR42)
  so PRD's cross-reference resolves
- AGENTS §6: remove 'tag sets' from Call 1 body description (Call 1 only uses
  species and attribute lists)
- PROMPTS.md: shipped defaults path corrected to backend/app/prompts/ (matches
  DEPLOYMENT repo layout)
- PROMPTS.md: Call 1 notes removed feat-* and fig-* from taxonomy list (Call 1
  returns free-text observations mapped to feat-* tags by server, not fig-*)
- PROMPTS.md: Call 2 template field names aligned with CONTENT-WOO defaults
  (width_avg_in, width_min_in, width_max_in, length_in_remainder)
- UX.md §112: remove 'tag lists' from Call 1 body description
- DATA-MODEL: prompt files location corrected from /data/prompts/ to
  backend/app/prompts/ (bind-mounted read-only to /app/prompts/)
- DEPLOYMENT: backup script updated (prompts are version-controlled in repo,
  no separate backup needed)
- docker-compose.yml: prompts mount corrected to ../backend/app/prompts

deploy/docker-compose.yml

@@ -31,7 +31,7 @@ services:
     volumes:
       - slab_db:/data
       - slab_images:/images
-      - ../prompts:/app/prompts:ro
+      - ../backend/app/prompts:/app/prompts:ro
     ports: ["127.0.0.1:${FASTAPI_PORT:-18081}:8000"]
     mem_limit: 2g
     restart: unless-stopped