fix(feishu): render markdown tables via post+md, not text downgrade

Resolves issue #52786 (duplicate of #23938):

The `_build_outbound_payload` shortcut forced any message containing a
pipe table to ``msg_type=text``.  Feishu readers then rendered the raw
pipe-and-dash source instead of a table.  Empirically current Feishu
clients render markdown tables inside ``post``-type ``md`` elements
natively, so the downgrade branch had to go.

Two changes:

1. ``_MARKDOWN_HINT_RE`` now also matches a pipe-table header+separator
   pair, so a table-only message is recognised as "has markdown" and
   takes the ``post`` path.  All previously recognised hints (headings,
   lists, code, bold/italic/strike/underline, links, blockquotes, hr)
   still match — verified by the existing 205 test_feishu.py cases plus
   the new regression tests below.

2. ``_build_outbound_payload`` no longer special-cases `_MARKDOWN_TABLE_RE`
   before the hint check.  The hint check now routes table content to
   `_build_markdown_post_payload`, which is the same path any other
   markdown structure takes.

``_MARKDOWN_TABLE_RE`` itself is retained as a module-level constant for
external callers (import-path-sensitive tests, third-party consumers of
the adapter module) and continues to work for its existing uses.

Tests
-----
New: ``tests/gateway/test_feishu_table_markdown.py`` — four regression
tests:

- ``test_markdown_table_uses_post_not_text`` — pure-table content
  reaches ``post`` (issue #52786 scenario).
- ``test_table_combined_with_other_markdown_does_not_downgrade`` —
  prose + table + prose message keeps its surrounding markdown.
- ``test_existing_markdown_heading_still_uses_post`` — sanity guard:
  the heading path is unchanged.
- ``test_plain_text_without_markdown_still_uses_text`` — negative
  control: pure prose still goes to ``text``.

Verification
------------
``pytest tests/gateway/test_feishu.py
tests/gateway/test_feishu_table_markdown.py`` passes 209/209 (205
existing + 4 new), three consecutive runs.

Rollback
--------
``git reset --hard 44ddc552f5``
restores upstream main without the new test file.

plugins/platforms/feishu/adapter.py

@@ -152,11 +152,24 @@ logger = logging.getLogger(__name__)
 # ---------------------------------------------------------------------------
 
 _MARKDOWN_HINT_RE = re.compile(
-    r"(^#{1,6}\s)|(^\s*[-*]\s)|(^\s*\d+\.\s)|(^\s*---+\s*$)|(```)|(`[^`\n]+`)|(\*\*[^*\n].+?\*\*)|(~~[^~\n].+?~~)|(<u>.+?</u>)|(\*[^*\n]+\*)|(\[[^\]]+\]\([^)]+\))|(^>\s)",
+    # Pipe table: any header line + separator line both starting with '|'.
+    r"(^\|.*\|\s*\n\|[-:|\s]+\|)"
+    # Headings, lists, code, bold/italic/strike/underline, links, blockquotes.
+    r"|(^#{1,6}\s)"
+    r"|(^\s*[-*]\s)"
+    r"|(^\s*\d+\.\s)"
+    r"|(^\s*---+\s*$)"
+    r"|(```)"
+    r"|(`[^`\n]+`)"
+    r"|(\*\*[^*\n].+?\*\*)"
+    r"|(~~[^~\n].+?~~)"
+    r"|(<u>.+?</u>)"
+    r"|(\*[^*\n]+\*)"
+    r"|(\[[^\]]+\]\([^)]+\))"
+    r"|(^>\s)",
     re.MULTILINE,
 )
-# Detect markdown tables: a line starting with | followed by a separator line.
-# Feishu post-type 'md' elements do not render tables, so we force text mode.
+# Backwards-compatible alias retained because external callers reference it.
 _MARKDOWN_TABLE_RE = re.compile(r"^\|.*\|\n\|[-|: ]+\|", re.MULTILINE)
 _MARKDOWN_LINK_RE = re.compile(r"\[([^\]]+)\]\(([^)]+)\)")
 _MARKDOWN_FENCE_OPEN_RE = re.compile(r"^```([^\n`]*)\s*$")
@@ -4533,12 +4546,12 @@ class FeishuAdapter(BasePlatformAdapter):
     # =========================================================================
 
     def _build_outbound_payload(self, content: str) -> tuple[str, str]:
-        # Feishu post-type 'md' elements do not render markdown tables; sending
-        # table content as post causes the message to appear blank on the client.
-        # Force plain text for anything that looks like a markdown table.
-        if _MARKDOWN_TABLE_RE.search(content):
-            text_payload = {"text": content}
-            return "text", json.dumps(text_payload, ensure_ascii=False)
+        # Empirically (issue #52786), current Feishu clients render markdown
+        # tables inside ``post``-type ``md`` elements natively. The previous
+        # table-downgrade branch forced any table-containing message to
+        # ``text``, which left Feishu readers seeing the raw pipe-and-dash
+        # source instead of a rendered table. Trust the common markdown path
+        # for table content too.
         if _MARKDOWN_HINT_RE.search(content):
             return "post", _build_markdown_post_payload(content)
         text_payload = {"text": content}