feat(pilotdeck): build Electron desktop app from source

Replace the prebuilt .deb web-only package with the real Electron
application built from upstream v2026.10.17:

- compile apps/desktop main process (tsc) and launch it with
  nixpkgs electron_42 in app-dir mode; upstream env overrides
  (PILOTDECK_DESKTOP_RUNTIME_ROOT, PILOTDECK_DESKTOP_NODE) select the
  staged runtime and bundled Node.js
- replicate the upstream runtime staging (build-runtime.mjs): prod-only
  hoisted node_modules from the dedicated runtime lockfile via a second
  fetchPnpmDeps, dist/skills/ui tree, source-import rewrite, pinned Cua
  driver, upstream runtime verification probes
- share electron-updater into the app by expanding pnpm virtual store
  scopes of its dependency closure
- wrap bin/pilotdeck (desktop, --no-sandbox, ozone hint auto) and keep
  bin/pilotdeck-server (headless web server) on the same runtime
- add pilotdeck.desktop entry, hicolor icon, startupWMClass

Verified: nix build passes, app launches under Xvfb reaching
"PilotDeck Web UI ready" with the window mapped as WM_CLASS
pilotdeck-desktop; headless server answers on :3001.

README.md

@@ -37,7 +37,7 @@ A custom Nix overlay and flake providing additional packages not found in upstre
 | `radar` | Modern Kubernetes visibility — topology, event timeline, service traffic, resource browsing, Helm management, and GitOps support | Kubernetes |
 | `omniroute` | Unified AI router with 160+ providers, auto fallback, MCP/A2A, OpenAI-compatible APIs | AI LLM Gateway |
 | `open-code-review` | AI-powered code review CLI combining deterministic pipelines with an LLM agent for line-level review comments | AI Coding Agents |
-| `pilotdeck` | Task-oriented AI Agent productivity platform (source-built web UI and gateway) with WorkSpace isolation, white-box memory, and smart routing | AI Agents |
+| `pilotdeck` | Task-oriented AI Agent productivity platform (source-built Electron desktop app, plus a headless server command) with WorkSpace isolation, white-box memory, and smart routing | AI Agents |
 | `relay-free-llm` | RESTful API to route user prompts to various AI model providers with automatic failover and intent-based routing | AI LLM Gateway |
 | `stakpak` | DevOps AI agent that generates infrastructure code, debugs Kubernetes, configures CI/CD, and automates deployments | AI Agents |
 | `traycer` | Open-source AI orchestration app for agentic coding | AI Coding Agents |
@@ -230,7 +230,7 @@ nix-overlay/
 │   ├── mcp-gateway/            # MCP protocol gateway
 │   ├── omniroute/              # Unified AI router with 160+ providers
 │   ├── open-code-review/       # AI code review CLI (deterministic + LLM agent)
-│   ├── pilotdeck/              # Task-oriented AI Agent platform (source-built web UI)
+│   ├── pilotdeck/              # Task-oriented AI Agent platform (source-built Electron desktop app)
 │   ├── radar/                  # Kubernetes UI (topology, timeline, Helm, GitOps)
 │   ├── relay-free-llm/        # AI model provider routing gateway
 │   ├── skillsmcp/              # MCP server for Agent Skills