Reduce code duplication and update README

- Extract shared utilities (HIDDEN_FILES, VIDEO_EXTENSIONS, fileApiUrl,
  thumbnailApiUrl, findFile) into new src/lib/media-utils.ts, removing
  identical copies from games.ts, movies.ts, tv.ts, files.ts, and scanner.ts
- Add comment in files.ts clarifying why its VIDEO_EXTENSIONS set intentionally
  differs from the media library set (web-playable formats for the mixed browser)
- Rewrite README to reflect the current feature set: Movies/TV libraries, auth
  system, tag system, background scanner, updated project structure, folder
  conventions for all four library types, and a complete API reference

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/tv.ts

@@ -2,39 +2,12 @@ import fs from 'fs'
 import path from 'path'
 import type { TvSeries, TvSeason, TvEpisode } from '@/types'
 import { parseTvShowNfo, parseEpisodeNfo } from './nfo'
-
-const HIDDEN_FILES = /^\./
-
-const VIDEO_EXTENSIONS = new Set(['.mkv', '.mp4', '.avi', '.mov', '.m4v', '.wmv', '.ts', '.m2ts'])
-
-function fileApiUrl(libraryId: string, relativePath: string): string {
-  return `/api/file?libraryId=${encodeURIComponent(libraryId)}&path=${encodeURIComponent(relativePath)}`
-}
-
-function thumbnailApiUrl(libraryId: string, relativePath: string): string {
-  return `/api/thumbnail?libraryId=${encodeURIComponent(libraryId)}&path=${encodeURIComponent(relativePath)}`
-}
+import { HIDDEN_FILES, VIDEO_EXTENSIONS, fileApiUrl, thumbnailApiUrl, findFile } from './media-utils'
 
 function isVideoFile(name: string): boolean {
   return VIDEO_EXTENSIONS.has(path.extname(name).toLowerCase())
 }
 
-/**
- * Finds the first file in a directory whose basename (without extension)
- * matches the given pattern (case-insensitive).
- */
-function findFile(dir: string, pattern: RegExp): string | null {
-  let entries: string[]
-  try {
-    entries = fs.readdirSync(dir)
-  } catch {
-    return null
-  }
-  return entries.find(
-    (e) => !HIDDEN_FILES.test(e) && pattern.test(path.basename(e, path.extname(e)))
-  ) ?? null
-}
-
 function readDirs(dir: string): string[] {
   try {
     return fs