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/files.ts

@@ -2,9 +2,10 @@ import fs from 'fs'
 import path from 'path'
 import type { DirectoryListing, FileEntry, MediaType } from '@/types'
 import { resolveAndJail } from '@/lib/libraries'
+import { HIDDEN_FILES, fileApiUrl, thumbnailApiUrl } from './media-utils'
 
-const HIDDEN_FILES = /^\./
-
+// Web-playable video formats for the Mixed Media browser (distinct from the
+// broader set used by dedicated movie/TV scanners).
 const VIDEO_EXTENSIONS = new Set(['.mp4', '.mov', '.mkv', '.avi', '.webm', '.m4v'])
 const IMAGE_EXTENSIONS = new Set(['.jpg', '.jpeg', '.png', '.gif', '.webp', '.bmp', '.tiff', '.tif'])
 
@@ -15,14 +16,6 @@ function getMediaType(filename: string): MediaType {
   return 'other'
 }
 
-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)}`
-}
-
 export function scanDirectory(
   libraryRoot: string,
   libraryId: string,