Fix analysis-quality test: strip literal [PLACEHOLDER] from propositions manifest

Agent-Logs-Url: https://github.com/Hack23/riksdagsmonitor/sessions/cd31fd04-e81b-4ac4-bc87-1b538d7b9743

Co-authored-by: pethers <1726836+pethers@users.noreply.github.com>

Author: Copilot

analysis/daily/2026-04-20/propositions/data-download-manifest.md

@@ -96,7 +96,7 @@
 Both articles have been validated for:
 - ✅ 0 `AI_MUST_REPLACE` markers.
 - ✅ 0 `TODO` placeholders.
-- ✅ 0 "[PLACEHOLDER]" patterns.
+- ✅ 0 bracketed "PLACEHOLDER" patterns.
 - ✅ All section numbers sequential.
 - ✅ All internal anchor links valid.
 - ✅ All external links use `rel="noopener"` where appropriate.