fix(hm): pass NonZeroU64 capacity to ImageRegistry::open in cache clean

main was broken: #117 changed ImageRegistry::open to take NonZeroU64, but the
cache-clean caller still passed u64::MAX (E0308). It slipped in as a semantic
merge (no textual conflict), so main's hm binary stopped compiling on stable.
This unbreaks main; every open PR is red only because GitHub builds them merged
with this broken main.

Author: markovejnovic

crates/hm/src/commands/cache/clean.rs

@@ -55,7 +55,7 @@ pub async fn handle_clean() -> Result<i32> {
 /// cache index is reset.
 async fn remove_registered_images(db_path: &std::path::Path) {
     // Capacity here is irrelevant — we only read existing rows, never insert.
-    let registry = match hm_vm::ImageRegistry::open(db_path, u64::MAX) {
+    let registry = match hm_vm::ImageRegistry::open(db_path, std::num::NonZeroU64::MAX) {
         Ok(r) => r,
         Err(e) => {
             tracing::warn!(error = %e, "could not open image registry; skipping image removal");