audit-3 (code cleanup): zero clippy warnings, zero build warnings

prep for deployment. cargo clippy --workspace --all-targets now passes
clean. cargo audit unchanged (same 2 unmaintained-warning macro-support
transitives; no cves).

cleanup applied:
- ProtocolParams construction in tools.rs uses struct-update syntax
  (clippy::field_reassign_with_default).
- main.rs collapsed two else-if branches with identical bodies
  (clippy::if_same_then_else).
- mint/plutus/stake sort_by(|a,b| b.cmp(&a)) → sort_by_key(Reverse(_))
  (clippy::manual_sort_by). 4 sites.
- metadata/mint/tx odd-length hex check uses .is_multiple_of(2)
  (clippy::manual_is_multiple_of). 3 sites.
- stake.rs witness_overhead conditional removed — both branches
  produced TWO_WITNESS_OVERHEAD_BYTES (left over from when
  registration was thought to add a third witness; it doesn't).
  WITNESS_OVERHEAD_BYTES const removed (only the two-witness one
  is used).
- Public spend/mint/stake build_signed_*_with_assets fns get
  #[allow(clippy::too_many_arguments)] — they ARE the API surface.
- ex_units_default_is_generous test gets explicit allow for the
  tautological-on-const assertion (kept the intent comment).

97 unit tests still pass. release build clean.

crates/aldabra-mcp/src/main.rs

@@ -82,9 +82,10 @@ async fn run() -> Result<()> {
     let (payment_key, stake_key, address) = {
         let root = if bootstrap_new {
             bootstrap::generate_and_save_root_key(&cfg.data_dir)?
-        } else if mnemonic_path.exists() {
-            bootstrap::load_or_create_root_key(&cfg.data_dir)?
-        } else if bootstrap_only {
+        } else if mnemonic_path.exists() || bootstrap_only {
+            // Both branches load (or create on the bootstrap path).
+            // `load_or_create_root_key` itself decides which based on
+            // whether `mnemonic.age` exists.
             bootstrap::load_or_create_root_key(&cfg.data_dir)?
         } else {
             anyhow::bail!(

crates/aldabra-mcp/src/tools.rs

@@ -826,8 +826,10 @@ impl WalletService {
         // verify script_data_hash. Hardcoded preprod value from
         // koios epoch_params; future improvement is pulling fresh
         // from the chain on each call. (PLUTUS-4 audit fix.)
-        let mut params = ProtocolParams::default();
-        params.plutus_v3_cost_model = Some(PLUTUS_V3_COST_MODEL_PREPROD.to_vec());
+        let params = ProtocolParams {
+            plutus_v3_cost_model: Some(PLUTUS_V3_COST_MODEL_PREPROD.to_vec()),
+            ..ProtocolParams::default()
+        };
 
         let cbor = build_signed_plutus_spend(
             &self.inner.payment_key,