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.

tests/test_forwarded_message_divider.py

@@ -0,0 +1,57 @@
+"""The thread parser must treat the Gmail-style "---------- Forwarded message
+---------" divider as a quote boundary, like "----- Original Message -----".
+
+`_ORIG_RE` already recognised the Japanese forward marker (転送) but not the
+English "Forwarded message" one, so forwarded mail produced by Odysseus itself
+(static/js/emailInbox.js emits exactly `---------- Forwarded message ----------`)
+leaked the divider into the level-0 reply bubble — or, with no Outlook header
+block to fall back on, was not split into turns at all.
+"""
+from src.email_thread_parser import parse_thread
+
+
+def test_forwarded_divider_not_leaked_into_reply_body():
+    text = (
+        "See below.\n\n"
+        "---------- Forwarded message ---------\n"
+        "From: Alice <alice@example.com>\n"
+        "Date: Thu, May 7, 2026 at 11:33 AM\n"
+        "Subject: Original subject\n"
+        "To: Bob <bob@x.com>\n\n"
+        "Forwarded body content.\n"
+    )
+    turns = parse_thread(None, text)
+    assert turns is not None
+
+    # The reply turn must be clean — the divider is noise, not reply content.
+    assert turns[0]["level"] == 0
+    assert "Forwarded message" not in turns[0]["body_html"]
+    # No turn at all should carry the raw divider in its rendered body.
+    assert all("Forwarded message" not in t["body_html"] for t in turns)
+
+    # The forwarded content becomes a deeper turn with sender meta.
+    deeper = [t for t in turns if t["level"] >= 1]
+    assert deeper, "forwarded body should split into a deeper turn"
+    assert "alice@example.com" in (deeper[0]["meta"] or "")
+    assert "Forwarded body content." in deeper[0]["body_html"]
+
+
+def test_forwarded_divider_alone_triggers_split():
+    # No Outlook header block — only the divider marks the forward. Before the
+    # fix this returned None (no split), folding the forward into the reply.
+    text = (
+        "See the message below.\n\n"
+        "---------- Forwarded message ----------\n"
+        "Forwarded body with no header block.\n"
+    )
+    turns = parse_thread(None, text)
+    assert turns is not None
+    assert any(t["level"] >= 1 for t in turns)
+    assert all("Forwarded message" not in t["body_html"] for t in turns)
+
+
+def test_forwarded_words_without_delimiters_do_not_split():
+    # Negative control: the bare words "forwarded message" in normal prose,
+    # with no [-_=]{3,} delimiters, must NOT be treated as a divider.
+    text = "I forwarded message after message to the team but heard nothing back."
+    assert parse_thread(None, text) is None