feat(server): TOOL_PACKS — advertise only the vertical packs a client uses

TOOL_PACKS=all (default) | comma list of core,pid. core is everything not
claimed by another pack and can never be dropped; unknown entries are
ignored with a warning. Pack hiding composes with TOOL_PROFILE=lean (the
lean set now carries pid_symbol_insert / pid_line_draw / pid_graph, 50
tools) and ENABLE_3D. system_about reports {enabled, available, ignored};
cad_batch's unknown_tool rejection names the TOOL_PACKS gate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

.env.example

@@ -55,6 +55,10 @@ DANGEROUS_COMMANDS_ENABLED=false
 # still boots, falling back to full with a warning.
 TOOL_PROFILE=full
 
+# Tool packs: all (default) | comma list of core,pid — advertise only the
+# vertical packs this client uses. core is always on.
+TOOL_PACKS=all
+
 # Tool discovery: off (default) | search
 # "search" replaces the advertised catalog with search_tools + call_tool, so a
 # client sees two tools instead of ~126 and searches by AutoCAD command name