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/server/app.ts

@@ -2,9 +2,9 @@ import express from 'express'
 import session from 'express-session'
 import path from 'node:path'
 import fsp from 'node:fs/promises'
-import { manifestRootPath, manifestDirPath, fileDirPath, viewsDirPath, publicDirPath } from '../shared/paths'
-import { indexRouter } from './routes/index'
-import { opRouter } from './routes/op'
+import { manifestRootPath, manifestDirPath, fileDirPath, viewsDirPath, publicDirPath } from '../shared/paths.js'
+import { indexRouter } from './routes/index.js'
+import { opRouter } from './routes/op.js'
 
 const PORT = Number(process.env.PORT ?? 3000)
 // 터미널에서 Ctrl+클릭으로 바로 열 수 있도록 기본값은 127.0.0.1.

src/server/routes/index.ts

@@ -1,5 +1,5 @@
 import { Router } from 'express'
-import { listPackKeys, loadPackDefinition, readManifest } from '../../shared/store'
+import { listPackKeys, loadPackDefinition, readManifest } from '../../shared/store.js'
 
 export const indexRouter = Router()
 

src/server/routes/op.ts

@@ -11,11 +11,11 @@ import {
   renamePack,
   sanitizePackKey,
   savePackList
-} from '../../shared/store'
-import { fetchReleaseVersions } from '../../shared/mojang'
-import { fetchPlaylistEntries, fetchVideoMeta, YtDlpUnavailableError } from '../youtube'
-import { requireAuth } from '../middleware/auth'
-import type { PackDefinition, PackList } from '../../shared/types'
+} from '../../shared/store.js'
+import { fetchReleaseVersions } from '../../shared/mojang.js'
+import { fetchPlaylistEntries, fetchVideoMeta, YtDlpUnavailableError } from '../youtube.js'
+import { requireAuth } from '../middleware/auth.js'
+import type { PackDefinition, PackList } from '../../shared/types.js'
 
 export const opRouter = Router()
 

src/server/youtube.ts

@@ -3,7 +3,7 @@ import { promises as fs, createWriteStream, constants as fsConst } from 'node:fs
 import path from 'node:path'
 import https from 'node:https'
 import http from 'node:http'
-import { getMcCustomDir } from '../shared/paths'
+import { getMcCustomDir } from '../shared/paths.js'
 
 export interface YtPlaylistEntry {
   id: string