…+ DingTalk markdown webhook

看板 SQLite 跨进程写锁（inter-process flock）：
Kanban SQLite cross-process write lock (inter-process flock):

问题：多个 kanban worker 进程并发写入同一 SQLite 数据库导致
WAL 损坏。SQLite WAL + busy_timeout 只能保护同一进程内的
并发线程，跨进程仍会竞争 BEGIN IMMEDIATE 导致页面损坏。

Problem: Multiple kanban worker processes writing concurrently to the
same SQLite database caused frequent WAL corruption. SQLite WAL +
busy_timeout only protects concurrent threads within the same process;
cross-process races through BEGIN IMMEDIATE can corrupt WAL pages.

修复：
Fix:
1. connect() 后打开 .db.lock 文件，write_txn() 用 fcntl.flock(LOCK_EX)
   包裹整个事务，确保同一时间只有一个进程在写。
2. schema init 也获取 .db.lock（不只是 .init.lock），防止 DDL/DML 竞争。
3. Windows 或 fcntl 不可用时优雅降级为 no-op。

1. After connect(), open a .db.lock file. Every write_txn() acquires
   fcntl.flock(LOCK_EX) around the entire transaction, ensuring only one
   process writes at a time.
2. Schema init also acquires .db.lock (not just .init.lock) to prevent
   DDL/DML races.
3. Graceful fallback on Windows or when fcntl is unavailable.

钉钉 webhook Markdown 渲染：
DingTalk webhook Markdown rendering:

问题：standalone cron delivery 用 msgtype:"text" 发钉钉消息，markdown
表格中的管道符显示为文字。live adapter 用 msgtype:"markdown" 正确渲染。

Problem: Standalone cron delivery sent msgtype:"text" for DingTalk, which
does not render markdown tables — pipes show as literal characters. The
live DingTalk adapter sends msgtype:"markdown" which renders tables correctly.

修复：统一使用 msgtype:"markdown"，被拒绝时 fallback 到纯文本。
Fix: Use msgtype:"markdown" consistently with fallback to plain text
if the API rejects the markdown payload.

Changes:
- hermes_cli/kanban_db.py: fcntl flock for inter-process write safety
- tools/send_message_tool.py: markdown msgtype for DingTalk standalone delivery

Related: NousResearch#35787 (closed), NousResearch#34400 (closed)