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/curate/mod.rs

@@ -148,7 +148,7 @@ impl Curator {
 // ---------------------------------------------------------------------------
 
 /// Crude token estimate: DeepSeek averages ~4 characters per token for English
-/// prose. Only used to size prompt budgets (§3.6 stage C).
+/// prose. Only used to size prompt budgets.
 pub fn approx_tokens(text: &str) -> usize {
     text.len().div_ceil(4)
 }
@@ -215,7 +215,7 @@ pub fn truncate_words(text: &str, max_words: usize) -> String {
     out
 }
 
-/// Truncate to roughly `max_tokens` tokens on a word boundary (§3.6 stage C).
+/// Truncate to roughly `max_tokens` tokens on a word boundary.
 pub fn truncate_tokens(text: &str, max_tokens: usize) -> String {
     let max_chars = max_tokens.saturating_mul(4);
     if text.len() <= max_chars {