Canadian cities labeler over Bluesky DMs

Users DM @cities.pds.cosocial.ca their city and get a signed account label.
Serves com.atproto.label.queryLabels and subscribeLabels, built on jacquard.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/bin/keygen.rs

@@ -0,0 +1,14 @@
+//! Generates the label signing key. The public multibase goes into the
+//! labeler's DID document as the `#atproto_label` verification method.
+use jacquard::common::types::crypto::multikey;
+use k256::ecdsa::SigningKey;
+use rand_core::OsRng;
+
+fn main() {
+    let key = SigningKey::random(&mut OsRng);
+    let public = key.verifying_key().to_encoded_point(true);
+    let multibase = multikey(0xE7, public.as_bytes());
+    println!("SIGNING_KEY_HEX={}", hex::encode(key.to_bytes()));
+    println!("# public key (did:key): did:key:{multibase}");
+    println!("# publicKeyMultibase:   {multibase}");
+}