CI (test shard 6) caught tests/tools/test_send_message_missing_platforms.py
importing the removed _send_dingtalk/_send_matrix helpers. Added thin
pre-migration-shaped shims around the plugins' _standalone_send (same pattern
mattermost/HA used in this file). Also restored access_token redaction in the
dingtalk plugin's _standalone_send error path (the legacy _send_dingtalk
returned via _error() which redacts URL secrets; the bare plugin return leaked
the webhook access_token in exception text) by reusing send_message_tool._error
via lazy import.
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