Feature: extended filter rules — attachment field + multi-value conditions

Adds an "Attachment" condition field (is present / of type <ext>) backed by
the RFC 5703 Sieve mime extension, matching the filename in both
Content-Disposition and Content-Type headers so real-world senders that only
put the name in Content-Type (Microsoft SMTPSVC, etc.) are caught. Users type
extensions (pdf, doc) not MIME types.

Also makes each text condition accept comma-separated multiple values emitted
as a Sieve string list (OR within the condition), so "(domain1 OR domain2)
AND attachment pdf/xml" is expressible in one rule. value is now string |
string[] (single-value rules stay strings -> backward compatible). New filter
locale keys in all 17 locales.

locales/en/common.json

@@ -1633,7 +1633,10 @@
       "actions": "Actions",
       "add_action": "Add Action",
       "stop_processing": "Stop processing subsequent rules",
+      "attachment_type_placeholder": "e.g. pdf, doc, jpg",
+      "value_placeholder_multi": "Value (multiple separated by commas)",
       "condition_fields": {
+        "attachment": "Attachment",
         "from": "From",
         "to": "To",
         "cc": "Cc",
@@ -1643,6 +1646,8 @@
         "body": "Body"
       },
       "comparators": {
+        "has_any": "is present",
+        "has_type": "of type",
         "contains": "contains",
         "not_contains": "does not contain",
         "is": "is exactly",