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

src/report.rs

@@ -22,7 +22,7 @@ pub enum RunStatus {
     /// Everything completed.
     Ok,
     /// The issue was produced but a best-effort stage failed (social, XTC,
-    /// world briefing, images) or the cost guardrail tripped (§3.6).
+    /// world briefing, images) or a provider budget tripped (§5).
     Degraded,
     /// No issue was produced.
     Failed,
@@ -98,7 +98,7 @@ pub struct StageCounts {
     pub clusters: i64,
     /// Admitted deep-set count retained for the colophon and runs table.
     pub candidates: i64,
-    /// Articles in the final lineup (§3.6 stage B).
+    /// Articles in the final lineup (§13).
     pub selected: i64,
     /// Discussion chapters rendered (§3.7).
     pub discussions: i64,