Move MCP tool description content into per-parameter descriptions

vault_patch's top-level MCP tool description was 3454 characters, well
over Claude Code's ~2KB truncation budget (#295) — the blank-line
warning was being silently cut off before it ever reached a session,
which had already caused a real content-gluing incident. Per-parameter
descriptions aren't subject to that truncation, so relocate content to
the field it actually describes: blank-line/separator behavior moves
to the content parameter, and marker-span semantics (what "marker"
covers for headings vs. block references, and the consequences of
omitting matching '#' depth or a trailing newline on a marker replace)
move to targetScope. This also removes duplication that had crept in
between the top-level prose and the field descriptions themselves.
vault_move gets the same treatment for consistency, though it was
never near the truncation limit.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>