new action: attach the message as PDF and file it

For senders whose mail body is the receipt (e.g. GoCardless payouts)
there is no attachment to file. The new action "Als PDF anhängen +
nach <Ordner>" renders the mail like a print from a mail client
(header block From/To/Date/Subject, then the content) and replaces it
in the target folder with: original content + PDF + the original mail
byte-for-byte as Original.eml, so the unaltered original is retained
(GoBD).

- Rendering with WeasyPrint. Images are fetched by us and inlined as
  data: URIs; WeasyPrint itself may only read data:. Fetching is
  restricted to http(s), public addresses (private, loopback,
  link-local and PDF_BLOCKED_NETWORKS, default 172.0.0.0/12, are
  refused; redirects are checked hop by hop), with time and size
  limits. cid: images come from the MIME parts.
- The replacement is APPENDed with the original flags and INTERNALDATE,
  verified in the target via its new Message-ID, and only then is the
  original deleted. Already converted mails are only moved.
- "PDF-Vorschau" in the rule dialog renders the newest matching mail
  read-only and opens it in the browser.
- List/log show 📄 targets; warnings for PDF + move/delete and for
  PDF + "Hat Anhang = Ja"; log folder search covers PDF targets.
- Docker image gets Pango and fonts (~316 MB total).

Tested with the real GoCardless mail (3 remote images, rendered both
locally and inside the built image) and a simulated IMAP server for
success, rejected APPEND, missing copy and already converted mails.

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

app/templates/logs.html

@@ -339,6 +339,7 @@ function emailOf(from) {
 function targetOf(log) {
     // Bei Aktionen steht der Zielordner in details, sonst Quellordner
     if (log.action_type === 'move' && log.details) return {text: '📁 ' + log.details.replace(/^INBOX[./]/, ''), filter: log.details};
+    if (log.action_type === 'pdf' && log.details) return {text: '📄 ' + log.details.replace(/^INBOX[./]/, ''), filter: log.details};
     if (log.action_type === 'forward' && log.details) return {text: '↪ ' + log.details, filter: null};
     if (log.action_type === 'delete') return {text: '🗑 Papierkorb', filter: null};
     if (log.folder) return {text: log.folder, filter: log.folder};
@@ -348,7 +349,7 @@ function targetOf(log) {
 function shortMessage(log) {
     const m = log.message || '';
     if (log.action_type && m.startsWith('Aktion ausgeführt')) {
-        return {move: 'Verschoben', forward: 'Weitergeleitet', delete: 'Gelöscht', mark_read: 'Als gelesen markiert'}[log.action_type] || m;
+        return {move: 'Verschoben', pdf: 'Als PDF angehängt & abgelegt', forward: 'Weitergeleitet', delete: 'Gelöscht', mark_read: 'Als gelesen markiert'}[log.action_type] || m;
     }
     return m;
 }