Phase 6: rules editor + unsubscribe detection (AUD-72)

- FR-11 rules editor: plain-text area at /rules, saved and versioned
  (SaveRules appends a version; restore re-saves an old version), parse
  errors surfaced, one-click re-classify. The reply model now reads the
  rules document too (FR-11).
- FR-7 unsubscribe: parse and store List-Unsubscribe / List-Unsubscribe-Post
  (migration v6), detect email and web links (internal/unsubscribe), a
  domain-level ignore list, and an explicit record of what was marked. No
  code path contacts an unsubscribe link; acting on one needs Sam's approval.
- Migration v6 is additive; unsubscribe gains url/updated_at.
- Tests: detector, parser, store migration/records/candidates, rules editor,
  unsubscribe handlers, message-detail rendering.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/mailfetch/fetch.go

@@ -102,18 +102,20 @@ func (f *Fetcher) Fetch(ctx context.Context) (Summary, error) {
 			headersSeen[parsed.SourceHeader] = struct{}{}
 		}
 		msg := &store.Message{
-			GmailID:         gmailID(r, uidValidity),
-			ThreadID:        r.GmailThreadID,
-			MessageIDHeader: parsed.MessageID,
-			FromAddr:        parsed.From,
-			ToAddr:          parsed.To,
-			Subject:         parsed.Subject,
-			BodyText:        parsed.BodyText,
-			SourceAddress:   parsed.SourceAddress,
-			DateSent:        parsed.Date,
-			ReceivedAt:      now,
-			IMAPUID:         int64(r.UID),
-			IMAPUIDValidity: int64(uidValidity),
+			GmailID:             gmailID(r, uidValidity),
+			ThreadID:            r.GmailThreadID,
+			MessageIDHeader:     parsed.MessageID,
+			FromAddr:            parsed.From,
+			ToAddr:              parsed.To,
+			Subject:             parsed.Subject,
+			BodyText:            parsed.BodyText,
+			SourceAddress:       parsed.SourceAddress,
+			ListUnsubscribe:     parsed.ListUnsubscribe,
+			ListUnsubscribePost: parsed.ListUnsubscribePost,
+			DateSent:            parsed.Date,
+			ReceivedAt:          now,
+			IMAPUID:             int64(r.UID),
+			IMAPUIDValidity:     int64(uidValidity),
 		}
 		if _, err := f.store.UpsertMessage(ctx, msg); err != nil {
 			return sum, err