Curation v2 step 4: triage replaces the gate

DeepSeek triage over every eligible article (plan §10) with cached
assessments in article_assessments, the union admission with quotas and
exploration slots (§11), hygiene moved to admit.rs with the churn rule
reading assessments, prefilter.rs reduced to hygiene and text heuristic,
prefilter_keep removed in favour of curation.ranking.deep_keep, the
scores table dropped (migration 0003), and --rescore on generate.

Implemented by Codex (gpt-5.4, high effort) from
docs/plans/curation-v2-briefs/step4.md; reviewed against plan §10–§11.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A1rCLQeKBgnBo3oTgHuTMe

migrations/0003_drop_scores.sql

@@ -0,0 +1 @@
+DROP TABLE scores;