Curation v2 step 7: cleanup, prune paths, implementation notes

Dead code and stale v1 comments removed (clippy -W dead_code clean, the
three world.rs warnings fixed), the Brief chapter's TOC title renamed from
"From the Editor", features prune now also sweeps article_assessments and
generate runs the sweep once after publishing, the example config is
tested key-for-key against Config::default(), README commands match
--help, and docs/plans/2026-08-15-implementation-notes.md records the
Anthropic and Voyage facts, the new tables, the budget-day rule and the
lock.

Implemented by a Claude agent from docs/plans/curation-v2-briefs/step7.md.

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

tests/m3_curation.rs

@@ -109,10 +109,10 @@ fn deep_messy_fixture_is_salvaged_not_rejected() {
     assert!(parse_deep_response("", &sections).is_empty());
 }
 
-/// Stage B responses must carry `{id, section, position, lead_story}` with
-/// exactly one lead, and use only palette section names (§3.6).
+/// Editor responses must carry `{id, section, position, lead_story}` with
+/// exactly one lead, and use only palette section names (plan §13).
 #[test]
-fn stage_b_fixture_parses_into_a_lineup() {
+fn editor_fixture_parses_into_a_lineup() {
     // The palette from `CurationConfig::default()` (§3.14).
     let sections = daily_epub::config::CurationConfig::default().sections;