fix data races in cache, resolver, qlog; add cache/zonefile/blocklist tests; update STATUS

- cache.Entry.Hits and LRU.perShard become atomics; SetCapacity now evicts
  down to the new budget; packKey fully qualifies names before packing
- resolver.Pool rewritten copy-on-write (atomic.Pointer to an immutable
  state); Upstream is immutable with shared *upstreamStats, so health
  survives a Rebind and the query path stops racing the config hook
- Pool.Exchange no longer marks a dead upstream healthy: Success was
  called before the error check, so the breaker never tripped
- qlog live ring publishes through atomic pointers
- blocklist.Holder.Get nil-safe; Builder lists each source once
- web: fix toast(string) misuse that rendered empty mutation toasts
- add unit tests for cache (with benchmarks) and zonefile
- STATUS.md: green -race integration suite, remaining failures and the
  broken bbolt snapshot round trip documented

internal/cache/cache.go

@@ -90,7 +90,9 @@ func canonical(name string) string {
 //
 //	varint len | wire name | uint16 type | uint16 class | uint8 flags
 func packKey(buf []byte, k Key) ([]byte, error) {
-	name := k.Name
+	// Keys are stored canonically (lowercase, no trailing dot) but the wire
+	// format needs a fully qualified name, so qualify it before packing.
+	name := dns.Fqdn(k.Name)
 	if n := len(name); n > 255*4 {
 		return nil, errKeyTooLong
 	}