Introduce the multi-file FastMCP layout. The mcp instance moves to _app.py
(imports nothing from tool modules, keeping the registration graph acyclic),
and the self-contained SpiceBook domain (5 tools + status resource + publish
prompt + 2 helpers) moves to spicebook_tools.py. server.py imports it for the
registration side effect.
Tool/resource/prompt counts unchanged (42/6/8); names identical. Repointed
test_spicebook's _read_netlist import. server.py: 2472 -> 2168 lines.