Follow-up to lkz-de's adapter chunking commit: long Signal messages no
longer truncate on ANY delivery path.
- tools/send_message_tool.py: register Signal's 8000-char limit in
_MAX_LENGTHS (imported from the adapter module so the two paths can't
drift) so hermes send / cron standalone / MCP sends split via the
shared truncate_message() pass instead of signal-cli rejecting them.
Standalone-path idea credited to @5L-hermes01 (#67279).
- tests: regression test proving standalone Signal sends chunk at the
adapter limit with no truncation footer (fails on pre-fix main).
- docs: Long Messages section on the Signal page (en + zh-Hans).
Both fixes verified by sabotage A/B (tests fail with the respective
half reverted to origin/main) and a real-import E2E: 27k-char message
with emoji + cross-boundary bold + code blocks -> 4 chunks, all styles
in-range UTF-16, lossless reassembly.
48f69e51d3