release: 2.0.1: DMARC ingest drops and bounds; Full backup from the panel

A patch on 2.0.0, all of it found on the test server after the cut:
  - a message that is not a report this relay keeps is dropped at once
    instead of being retried for days;
  - a report is bounded before it is stored, and reports are kept per
    domain (security review of the ingest path, nothing Critical or High);
  - Full backup from the panel works (it had answered 200 with ten bytes
    since 1.3.0);
  - no backup holds the Postfix queue, and the panel says why.

Cut: CHANGELOG [Unreleased] -> [2.0.1]; image pin 2.0.1 in compose,
README, guide; version table.

On the test server, on dd0fefd: go vet ./... ok, go test ./... ok
(22 packages), make e2e ok.

Full detail: CHANGELOG.md (2.0.1).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,8 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ## [Unreleased]
 
+## [2.0.1] - 2026-10-11
+
 ### Changed
 
 - **A message that is not a report this relay keeps is dropped at once.**