fix(signal): correct SPOILER docstring + AUTHOR_MAP for exiao

- _markdown_to_signal docstring claimed SPOILER support but the regex list
  never handled ``||...||``. Correct the docstring to match the four
  actually-supported styles (BOLD / ITALIC / STRIKETHROUGH / MONOSPACE).
  Signal's SPOILER bodyRange would need dedicated ``||spoiler||`` parsing
  and is left for a follow-up.

- scripts/release.py: add exiao's noreply email to AUTHOR_MAP so the
  contributor-attribution gate accepts their cherry-picked commit.

gateway/platforms/signal.py

@@ -737,7 +737,9 @@ class SignalAdapter(BasePlatformAdapter):
         Positions are measured in **UTF-16 code units** (not Python code
         points) because that's what the Signal protocol uses.
 
-        Supported styles: BOLD, ITALIC, STRIKETHROUGH, MONOSPACE, SPOILER.
+        Supported styles: BOLD, ITALIC, STRIKETHROUGH, MONOSPACE.
+        (Signal's SPOILER style is not currently mapped — no standard
+        markdown syntax for it; would need ``||spoiler||`` parsing.)
 
         Returns ``(plain_text, styles_list)`` where *styles_list* may be
         empty if there's nothing to format.

scripts/release.py

@@ -44,6 +44,7 @@ AUTHOR_MAP = {
     "qiyin.zuo@pcitc.com": "qiyin-code",
     "teknium@nousresearch.com": "teknium1",
     "127238744+teknium1@users.noreply.github.com": "teknium1",
+    "2093036+exiao@users.noreply.github.com": "exiao",
     "revar@users.noreply.github.com": "revaraver",
     # Matrix parity salvage batch (April 2026)
     "sr@samirusani": "samrusani",