Email: recognize forwarded message dividers

`_ORIG_RE` (and its JS mirror `_TALON_ORIG_RE`) already recognised the
Japanese forward marker `転送` alongside the "Original Message" delimiters,
but not the English "Forwarded message" one. So Gmail-style forwards —
including the ones Odysseus itself emits (`---------- Forwarded message
----------`, static/js/emailInbox.js) — were not treated as a quote
boundary:

  - with a following Outlook From:/Date: header block, the divider line
    leaked into the level-0 reply bubble as noise;
  - with only the divider marking the forward (no header block), the body
    was not split into turns at all.

Add `Forwarded\s+message` to the same `[-_=]{3,}`-delimited alternation in
both the server-side parser and the JS mirror, so forward dividers are
consumed as an attribution boundary like "----- Original Message -----".
Locale variants of "Forwarded message" can follow the existing pattern.

Tests cover both manifestations plus a negative control (the bare words
"forwarded message" without `[-_=]{3,}` delimiters must not split).

Checks: python -m pytest tests/test_forwarded_message_divider.py (3 passed),
python -m py_compile src/email_thread_parser.py, node --check
static/js/emailLibrary/utils.js, git diff --check.

src/email_thread_parser.py

@@ -57,7 +57,8 @@ _CCBCC = r"(?:Cc|Bcc|Kopie|Skrytá kopie|Копия)"
 _HDR_KEYS = rf"(?:{_FROM}|{_SENT}|{_SUBJ}|{_TO}|{_CCBCC}|Importance|Priority)"
 
 _ORIG_RE = re.compile(
-    r"(?:^|\n)[\s>]*[-_=]{3,}\s*(?:Original\s+Message|Ursprüngliche\s+Nachricht|"
+    r"(?:^|\n)[\s>]*[-_=]{3,}\s*(?:Original\s+Message|Forwarded\s+message|"
+    r"Ursprüngliche\s+Nachricht|"
     r"Mensaje\s+original|Messaggio\s+originale|Message\s+d['’]origine|"
     r"Oorspronkelijk\s+bericht|Original\s+meddelande|原文|原始邮件|転送)"
     r"\s*[-_=]{3,}",