docs: archive the screenshot-automation plan as rejected

The Playwright screenshot pipeline is not being built: screenshots are
the only doc format no gate can verify, they rot silently at every UI
change, and a redesign was the stated plan. Replaced by
docs/developer/writing-ui-docs.md (pattern-first text, exact quoted
labels enforced by TestUIControlLabels) — see that page for the full
reasoning. Body kept below unmodified for history.

SCREENSHOT_AUTOMATION.md

@@ -1,6 +1,14 @@
 # Screenshot Automation Plan for Bookhoard Documentation
 
-> **Status**: Ready to implement when frontend is complete  
+> **Status**: REJECTED / ARCHIVED (2026-11-02) — not implementing.
+> **Superseded by**: [docs/developer/writing-ui-docs.md](docs/developer/writing-ui-docs.md) —
+> Bookhoard docs are written screenshot-free from now on. Why: screenshots go
+> stale silently (no gate can diff pixels against the UI), die on every
+> redesign, and are unverifiable; the UI is server-rendered so exact labels are
+> greppable and gate-checked instead (`TestUIControlLabels`). The prose
+> standard teaches patterns that survive re-layouts. Kept below unmodified for
+> history.
+>
 > **Last Updated**: 2026-02-03
 
 This document outlines the complete plan for automatically generating screenshots for Bookhoard documentation using Playwright.