v2.0.0: SDK v2, dual-era MCP, Cornerstone3D 5.13.1

The MCP server moves to the SDK v2 packages and protocol revision 2026-07-28 while still serving hosts on the 2025-11-25 handshake: one server, both eras, verified with the smoke test under each era and with an SDK 1.x client. The agent server needs Node 20 or later; the viewer stays on Node 22 or later. The fifteen verbs, the resources, the prompts and the fence are unchanged.

• SDK v2, dual-era stdio: @modelcontextprotocol/server 2.4.0, Zod 4; input schemas now advertise JSON Schema 2020-12.
• Cornerstone3D 5.6.12 to 5.13.1: all eight reading modes re-verified. ROI density statistics now count exactly the voxels inside the drawn region (the old build counted one extra edge row and column); areas, min and max are unchanged.
• Fix: the Pan, Zoom, StackScroll, Length and Angle tools were never registered with the engine, so Length and Angle could not draw. They do now.
• Smoke test: runs once per protocol era (--era= for one) and forwards the viewer URL to the server.
• Dependencies and CI: vitest 5, lucide-react 1.59, actions/checkout v7, actions/setup-node v7, gitleaks-action v3, all pinned to commit SHAs.

cbctscope-2.0.0.mcpb installs the agent half for Claude Desktop; the viewer runs from this repository.