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/message_test.go

@@ -172,3 +172,34 @@ func TestHeaderAddressParsing(t *testing.T) {
 		}
 	}
 }
+
+func TestParseMessageCapturesUnsubscribeHeaders(t *testing.T) {
+	raw := "From: Heritage Fruit Trees <support@heritagefruittrees.com.au>\r\n" +
+		"To: samuelrolfe@gmail.com\r\n" +
+		"X-Pm-Original-To: hello@where-woof.com\r\n" +
+		"Subject: New workshops\r\n" +
+		"List-Unsubscribe: <mailto:unsub@heritagefruittrees.com.au?subject=unsubscribe>, <https://heritagefruittrees.com.au/u?id=1>\r\n" +
+		"List-Unsubscribe-Post: List-Unsubscribe=One-Click\r\n" +
+		"Message-Id: <abc@mail.example>\r\n" +
+		"Date: Mon, 01 Jan 2026 10:00:00 +0000\r\n" +
+		"Content-Type: text/plain; charset=utf-8\r\n" +
+		"\r\n" +
+		"Hello, you can unsubscribe at https://heritagefruittrees.com.au/u?id=1.\r\n"
+
+	pm, err := ParseMessage([]byte(raw))
+	if err != nil {
+		t.Fatalf("ParseMessage() error = %v", err)
+	}
+	if !strings.Contains(pm.ListUnsubscribe, "mailto:unsub@heritagefruittrees.com.au") {
+		t.Errorf("ListUnsubscribe = %q", pm.ListUnsubscribe)
+	}
+	if !strings.Contains(pm.ListUnsubscribe, "https://heritagefruittrees.com.au/u?id=1") {
+		t.Errorf("ListUnsubscribe = %q", pm.ListUnsubscribe)
+	}
+	if pm.ListUnsubscribePost != "List-Unsubscribe=One-Click" {
+		t.Errorf("ListUnsubscribePost = %q", pm.ListUnsubscribePost)
+	}
+	if pm.SourceAddress != "hello@where-woof.com" {
+		t.Errorf("SourceAddress = %q", pm.SourceAddress)
+	}
+}