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

docs/DATA-MODEL.md

@@ -194,10 +194,11 @@ Sheet/slider prefs (`sheet_mode`, sensitivity, edge offset, feather) are **not**
 settings keys in POC. Client localStorage is source of truth (AGENTS §4 / ARCHITECTURE §5).
 Optional server sync of those prefs is out of scope for POC.
 
-**Prompt files** — not in the settings table. Stored as text files in
-`/data/prompts/` (server volume). Read fresh on each invocation. Default
-prompts shipped with the app; owner edits directly. A reset-to-default script
-restores originals.
+**Prompt files** — not in the settings table. Shipped as text files in
+`backend/app/prompts/` (repo), bind-mounted read-only to `/app/prompts/` in the
+FastAPI container. Read fresh on each invocation. Default prompts shipped with the
+app; owner edits on the host; no restart needed. A reset-to-default script
+restores originals from the app bundle.
 
 This table is the ciphertext **key inventory** and schema only. The never-browser /
 AES-GCM / `SLAB_AES_KEY` env policy lives in AGENTS.md §4; flow lives in ARCHITECTURE §5.