Tag Sink links with the !path sender

[sg]

What changed

• shorten() takes a sender argument; !path passes the same name its reply is addressed to.
• Sink links gain a from:<sender> tag alongside mcbot and path, so the dashboard tag filter shows who generated a map.

Why

• The from: prefix keeps a sender named like a command (e.g. "Path") distinct — Sink lowercases and de-duplicates tags, which would otherwise merge the two silently.
• Names are trimmed to Sink's 32-character tag limit, measured in UTF-16 code units the way zod counts them. An emoji costs 2, and Sink rejects the entire create if any tag is over — which would drop that sender to the da.gd fallback rather than just losing a tag. Mesh node names carry emoji often enough to matter.

Verified end-to-end against the live instance: plain, spaces/apostrophe/emoji, 60-char, 27-emoji, sender named "path", and no-name all created successfully with correct tags. !topo is unchanged (passes no sender); one argument away if wanted.

Breaking changes

None. Only affects the sink provider; dagd and none ignore the argument.