Curation v2 step 3: Voyage embeddings, cheap signals, candidate telemetry

- embedding.rs: EmbeddingBackend + VoyageBackend, batched bounded-concurrency
  client with its own UsageMeter, f32 BLOB codec, article/interest embedding
  cache keyed by model, dimension and sha256 of the embedded text.
- signals.rs: z-scored interest match, decayed rated-neighbour preference
  with the knn gate, feed affinity with the feed gate, social, text heuristic
  without social terms, mid-rank percentile normalizer, preliminary blend.
- telemetry.rs: candidate_runs writer with §7.5 signals_json, explain and
  near-misses renderers, prune.
- [voyage] and the full [curation.ranking] config with validation.
- CLI: explain, features backfill|prune, generate --skip-embeddings.
- Pipeline: hygiene rows, embed and signals stages before the old prefilter;
  same-date regeneration no longer excludes its own picks.

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

src/curate/profile/mod.rs

@@ -125,6 +125,16 @@ pub fn load_profile(path: &Path) -> anyhow::Result<ProfileFile> {
     }
 }
 
+/// Load the exact standing-interest union used in the system prompt.
+pub fn load_standing_interests(
+    opml_path: &Path,
+    profile_path: &Path,
+) -> anyhow::Result<Vec<String>> {
+    let opml = parse_interests(opml_path)?;
+    let profile = load_profile(profile_path)?;
+    Ok(union_interests(opml, profile.interests))
+}
+
 fn union_interests(opml: Vec<String>, profile: Vec<String>) -> Vec<String> {
     let mut seen = BTreeSet::new();
     let mut out = Vec::new();