feat: Enhance NodeCG process management and add IPC security tests

docs/refactor/PHASE_2_SUMMARY.md

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+# Phase 2 Summary
+
+## Scope
+
+Executed the IPC and process-management phase only.
+
+Documentation used as source of truth:
+
+- `docs/refactor/ARCHITECTURE_AUDIT.md`
+- `docs/refactor/ARCHITECTURE_RULES.md`
+- `docs/refactor/TARGET_ARCHITECTURE.md`
+- `docs/refactor/MIGRATION_PLAN.md`
+- `docs/refactor/SESSION_HANDOFF.md`
+
+## IPC And Preload Decision
+
+No IPC or preload layer was added.
+
+This is intentional. The current architecture defines a zero-surface IPC model as the secure target because there is no custom renderer and no product requirement for desktop APIs to cross into web content.
+
+To make that decision enforceable, a regression test now scans `src/main` and fails if main-process source introduces:
+
+- `ipcMain`
+- `ipcRenderer`
+- `contextBridge`
+- `preload`
+
+## Process Management Changes
+
+- Narrowed `NodecgProcessManager` so `startNodecgProcess` no longer returns the raw `ChildProcess`.
+- Removed the public internal `getProcess` escape hatch from `NodecgProcessManager`.
+- Added explicit NodeCG process states:
+  - `idle`
+  - `starting`
+  - `running`
+  - `stopping`
+  - `stopped`
+  - `failed`
+- Added `getState` as the narrow observable process-management API.
+- Made NodeCG startup idempotent while an async startup is already in progress.
+- Prevented new startup while process shutdown is in progress.
+- Preserved process-tree termination through `platform-process-killer.ts`.
+- Preserved `ELECTRON_RUN_AS_NODE`, `shell: false`, `windowsHide: true`, and detached POSIX process-group behavior.
+
+## Security Notes
+
+- No raw Electron IPC APIs are imported in production source.
+- No preload script is configured or exposed.
+- No renderer/main business logic boundary was added.
+- No filesystem, process, shell, or update primitives were exposed to web content.
+- BrowserWindow security settings from Phase 1 remain unchanged.
+
+## Verification
+
+Commands run successfully:
+
+```text
+npm run typecheck
+npm test
+npm run lint
+```
+
+Current test result:
+
+```text
+55 tests passing
+```
+
+Additional sanity search:
+
+```text
+rg -n "ipcMain|ipcRenderer|contextBridge|preload|nodeIntegration:\s*true|webSecurity:\s*false|\bany\b" src/main src/tests
+```
+
+Result:
+
+- No production IPC or preload surface exists.
+- No unsafe Electron settings were introduced.
+- Remaining IPC/preload string matches are limited to the regression test that guards the zero-surface policy.