Add Phase B: cookies, aria2c, proxy/rate-limit, restrict-filenames & archive

Implements the remaining Phase B (Access & networking) items from
ROADMAP.md: cookie sources (browser cookie-store import, or a built-in
sign-in window that exports a Netscape cookie file via a persisted Electron
session partition), the aria2c external downloader, proxy/rate-limit,
restrict-filenames, and a download-archive to skip repeats.

Wires download.ts to the buildArgs() module added in the previous commit
(it wasn't hooked up yet) and renames its options param
NetworkOptions -> AccessOptions to reflect the wider scope now that cookies
and filename/archive flags joined proxy/rate-limit/aria2c.

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

src/shared/ipc.ts

@@ -20,7 +20,10 @@ export const IpcChannels = {
   historyRemove: 'history:remove',
   historyClear: 'history:clear',
   /** main → renderer push channel for live download events */
-  downloadEvent: 'download:event'
+  downloadEvent: 'download:event',
+  cookiesLogin: 'cookies:login',
+  cookiesStatus: 'cookies:status',
+  cookiesClear: 'cookies:clear'
 } as const
 
 /** Sentinel format id meaning "let yt-dlp pick the best video+audio". */
@@ -45,6 +48,17 @@ export const VIDEO_CODECS: VideoCodecPref[] = ['any', 'h264', 'vp9', 'av1']
 /** Whether SponsorBlock cuts the segments out or just marks them as chapters. */
 export type SponsorBlockMode = 'remove' | 'mark'
 
+/**
+ * Where yt-dlp's auth cookies come from. 'browser' reads a logged-in browser's
+ * cookie store directly; 'login' uses a cookie file exported from AeroFetch's
+ * own built-in sign-in window (see src/main/cookies.ts).
+ */
+export type CookieSource = 'none' | 'browser' | 'login'
+
+/** Browsers yt-dlp's --cookies-from-browser supports that ship on Windows. */
+export const COOKIE_BROWSERS = ['chrome', 'edge', 'firefox', 'brave', 'opera', 'vivaldi'] as const
+export type CookieBrowser = (typeof COOKIE_BROWSERS)[number]
+
 /** SponsorBlock segment categories (subset of yt-dlp's, the ones Seal exposes). */
 export const SPONSORBLOCK_CATEGORIES = [
   'sponsor',
@@ -234,6 +248,35 @@ export interface Settings {
   clipboardWatch: boolean
   /** default post-processing / format options for new downloads */
   downloadOptions: DownloadOptions
+  /** yt-dlp --proxy value, e.g. 'socks5://127.0.0.1:1080'. Empty disables it. */
+  proxy: string
+  /** yt-dlp --limit-rate value, e.g. '2M' or '500K'. Empty means unlimited. */
+  rateLimit: string
+  /** use bundled aria2c (resources/bin/aria2c.exe) as the external downloader */
+  useAria2c: boolean
+  /** where auth cookies come from: none, a browser's store, or the sign-in window */
+  cookieSource: CookieSource
+  /** which browser to read cookies from when cookieSource is 'browser' */
+  cookiesBrowser: CookieBrowser
+  /** sanitize output filenames to a portable ASCII-only subset (--restrict-filenames) */
+  restrictFilenames: boolean
+  /** record completed downloads in a yt-dlp --download-archive file to skip repeats */
+  downloadArchive: boolean
+}
+
+/** Whether the built-in sign-in window has ever saved a cookie file, and when. */
+export interface CookiesStatus {
+  exists: boolean
+  /** epoch milliseconds the cookie file was last written */
+  savedAt?: number
+}
+
+/** Result of a built-in sign-in window session, resolved once the window closes. */
+export interface CookiesLoginResult {
+  ok: boolean
+  /** number of cookies captured into the exported file */
+  cookieCount?: number
+  error?: string
 }
 
 /** A completed download, persisted to history.json (newest-first). */