Migrate tsconfig to Node16 module/moduleResolution

VS Code surfaced the TS deprecation:
  'moduleResolution=node10' is deprecated and won't work in TS 7.0.

Fix: switch the root tsconfig.json from
  module: CommonJS, moduleResolution: node
to
  module: Node16, moduleResolution: Node16

TypeScript 7 only supports node16/nodenext/bundler. node16 matches the
runtime semantics we already use (Node ≥ 16, CommonJS output via the
absence of "type": "module" in package.json), so the emit is unchanged.

Side effect of Node16 resolution: relative imports must carry the .js
extension. Added .js to every relative import across src/* (17 sites,
8 files). Bare module specifiers (express, electron, node:fs, ...) are
unaffected.

Verified:
- tsc -p tsconfig.server.json — 0 errors
- tsc -p tsconfig.installer.json — 0 errors
- node dist/server/app.js boots; /op login → 302, /op/list → 200

src/installer/main.ts

@@ -16,9 +16,9 @@ import type {
   PortForwardResult,
   RamCheckResult,
   ServerInstallPayload
-} from './types'
-import type { Manifest, PackDefinition } from '../shared/types'
-import { normalizePackDefinition } from '../shared/store'
+} from './types.js'
+import type { Manifest, PackDefinition } from '../shared/types.js'
+import { normalizePackDefinition } from '../shared/store.js'
 
 interface InstallerState {
   manifestUrl: string

src/installer/preload.ts

@@ -1,5 +1,5 @@
 import { contextBridge, ipcRenderer } from 'electron'
-import type { ClientInstallPayload, FetchedPack, RamCheckResult, ServerInstallPayload, PortForwardResult } from './types'
+import type { ClientInstallPayload, FetchedPack, RamCheckResult, ServerInstallPayload, PortForwardResult } from './types.js'
 
 const api = {
   // 1단계

src/installer/types.ts

@@ -1,4 +1,4 @@
-import type { Manifest, PackDefinition } from '../shared/types'
+import type { Manifest, PackDefinition } from '../shared/types.js'
 
 export interface InstallerConfig {
   manifestUrl: string