fix: harden payment flows and startup migrations

This closes replay and accounting gaps, makes billing and webhook state deterministic, and makes SQLite startup upgrades fail loudly instead of silently continuing on drifted schemas.

Author: Kenbak

ROADMAP.md

@@ -15,14 +15,15 @@ pub fn derive_invoice_address(key_str: &str, index: u32) -> Result<DerivedAddres
     let raw = addr.to_raw_address_bytes();
     let orchard_receiver_hex = hex::encode(raw);
 
-    let ua = zcash_address::unified::Address::try_from_items(vec![
-        Receiver::Orchard(raw),
-    ])
-    .map_err(|e| anyhow::anyhow!("UA construction failed: {:?}", e))?;
+    let ua = zcash_address::unified::Address::try_from_items(vec![Receiver::Orchard(raw)])
+        .map_err(|e| anyhow::anyhow!("UA construction failed: {:?}", e))?;
 
     let ua_string = ua.encode(&network);
 
-    tracing::debug!(diversifier_index = index, "Derived invoice address from viewing key");
+    tracing::debug!(
+        diversifier_index = index,
+        "Derived invoice address from viewing key"
+    );
 
     Ok(DerivedAddress {
         ua_string,