feat: implement Model Context Protocol (MCP) server & graceful in-place installer updates

[spelech]

Summary

This PR implements an official Model Context Protocol (MCP) server for AI agent integration and provides robust in-place update support across all Windows and Linux installation/upgrade pipelines.

🌟 Key Changes

1. Model Context Protocol (MCP) Server (/mcp & /api/mcp/tools):

   • Integrated ModelContextProtocol.AspNetCore v2.2.0.
   • Added LocalLlmMcpTools exposing 8 AI automation tools:
     • get_gpu_vram — Real-time GPU VRAM telemetry via NVML CUDA.
     • check_health — Probe Ollama (:11434), SD Forge (:7860), and ComfyUI (:8188).
     • list_models — Installed Ollama models, quantization tags, and footprints.
     • pull_model — Automated model pull from Ollama library / Hugging Face.
     • unload_vram — Release loaded models from GPU VRAM (keep_alive: 0).
     • start_engine / stop_engine — Manage SD Forge and ComfyUI backend processes.
     • detect_tools — Auto-scan drives and PATH for installed tools.
   • Mapped /mcp Streamable HTTP & SSE transport endpoint and updated GET /api/mcp/tools discovery.

2. In-Place Installer & Update Lifecycle:

   • Inno Setup (scripts/installer.iss): Adds CloseApplications=yes, graceful service shutdown (net stop) & process termination before file copy to eliminate Windows file locking errors, preserves settings.json with onlyifdoesntexist, and reconfigures/starts service post-install.
   • PowerShell Install/Update (scripts/install.ps1, scripts/update.ps1): Added active service detection, tray process kill, atomic settings.json backup/restore, and service/tray app restart.
   • Linux Installer (scripts/install_linux.sh): Added systemctl is-active detection, service teardown, config preservation, and automatic systemd restart.

3. Quality Assurance & Traceability:

   • Added McpServerIntegrationTests.cs (22 tests) covering DI resolution, attributes, tool execution, and error handling.
   • Updated README.md, docs/REQUIREMENTS.md (RTM), docs/TEST_COVERAGE.md, and docs/ARCHITECTURE.md.
   • All 174 tests in the test suite pass (173 passed, 1 skipped screenshot doc generator, 0 failed).