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

config.py

@@ -102,6 +102,10 @@ class Settings:
         # server.REMOVED_TOOL_PROFILES).
         self.tool_profile: str = os.environ.get("TOOL_PROFILE", "full").lower().strip()
 
+        # Tool packs: "all" (default) advertises every vertical pack; a comma
+        # list ("core,pid") advertises only those. core cannot be disabled.
+        self.tool_packs: str = os.environ.get("TOOL_PACKS", "all").lower().strip()
+
         # Tool discovery: "off" (default) advertises the full catalog; "search"
         # replaces it with a search tool plus a call_tool proxy (see
         # discovery/transform.py and server._apply_discovery_mode).