#3: close 3 known F1 gaps - folder/mailbox counters, quota-at-RCPT, alias fan-out

Per feature/3-f0-f1-validation's own gap analysis (commit 097fa37):

- InboundMessageRepository.Persist now updates folders.unread_count,
  folders.total_count, and mailboxes.used_bytes in the same transaction
  as the message insert (PLAN.md section 6.1 "++counters" was a no-op
  before this).
- MailboxRecord carries QuotaBytes/UsedBytes; ResolveRecipient rejects
  RCPT with 452 4.2.2 when a target mailbox has already reached its
  quota (used_bytes >= quota_bytes), before DATA - never silently
  accepting mail into a full mailbox.
- MailboxRepository.ResolveDeliveryTargets tries a direct mailbox match
  first, then falls back to the aliases table (exact source_address
  match takes precedence over a domain catch-all). One RCPT TO can now
  fan out to multiple mailboxes; alias destinations that don't resolve
  to an internal active mailbox are silently skipped, since outbound/
  external forwarding doesn't exist yet. postmaster@/abuse@/dmarc@-style
  aliases now actually deliver.

The E2E test's counters_updated subtest flips from a documented KNOWN
GAP (t.Skipf) to a hard assertion now that it passes, and gains two new
subtests (quota_rejected_when_mailbox_full, alias_resolves_to_destination_mailbox)
covering the other two fixes end-to-end. New unit and Postgres
integration test coverage added for all three fixes at every layer.

Verified: full suite green on Windows (unit + E2E via embedded
Postgres, no Docker needed) and via WSL Docker against the real
docker-compose Postgres (all infrastructure/postgres and diskstorage
integration tests, not just E2E). lang-lint clean.

services/protocols/internal/application/port/mailbox_repository.go

@@ -12,11 +12,23 @@ import (
 type MailboxRecord struct {
 	ID              uuid.UUID
 	MaxMessageBytes int64
+	QuotaBytes      int64
+	UsedBytes       int64
 }
 
-// MailboxRepository resolves a recipient address to an active mailbox.
+// MailboxRepository resolves a recipient address to the active mailbox(es)
+// mail for it should be delivered to.
 type MailboxRepository interface {
 	// FindActiveByAddress returns nil, nil (not an error) when no active
 	// mailbox with an active domain matches address.
 	FindActiveByAddress(ctx context.Context, address string) (*MailboxRecord, error)
+
+	// ResolveDeliveryTargets returns every active mailbox mail for address
+	// should be delivered to: the mailbox itself when address matches one
+	// directly, or the mailbox(es) reached through a matching alias
+	// (source_address exact match takes precedence over a domain
+	// catch-all). Returns an empty, non-nil slice (not an error) when
+	// nothing matches - a direct mailbox miss, an alias with no active
+	// destination, or no alias at all are all "not found", not failures.
+	ResolveDeliveryTargets(ctx context.Context, address string) ([]MailboxRecord, error)
 }