Separate per-kind video/audio folders, defaulting to Documents\Video and Documents\Audio

Existing installs had outputDir persisted to the Downloads folder (auto-filled by
earlier versions), so the v0.3.0 per-kind routing never triggered — downloads kept
going to Downloads. Replace the single outputDir setting with independent videoDir
and audioDir settings:

- Settings model: drop Settings.outputDir; add videoDir + audioDir (both blank by
  default). A blank value routes that kind into Documents\Video / Documents\Audio;
  a chosen folder overrides it. The stale outputDir key in old settings files is
  simply ignored, so existing users now get the Documents defaults.
- buildCommand routes by kind: per-download override → per-kind folder → default.
- The renderer no longer sends a global outputDir, so main always routes by kind.
- Settings: the single "Download folder" field becomes separate "Video folder" and
  "Audio folder" pickers, each with a Browse + Reset and a Documents\… placeholder.
  Store gains chooseDir(target) / clearDir(target).
- Onboarding: replace the folder picker with a short note about the two default
  folders (changeable in Settings).
- Bump version to 0.3.1.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/settings.ts

@@ -17,7 +17,10 @@ import {
 } from '@shared/ipc'
 
 const DEFAULTS: Settings = {
-  outputDir: '', // blank = route by kind into Documents\Video / Documents\Audio (see getDefaultMediaDir)
+  // Both blank by default → downloads land in Documents\Video / Documents\Audio
+  // (see getDefaultMediaDir). A non-empty value is an explicit per-kind override.
+  videoDir: '',
+  audioDir: '',
   defaultKind: 'video',
   defaultVideoQuality: 'Best available',
   defaultAudioQuality: 'Best (MP3)',
@@ -126,9 +129,9 @@ export function getSettings(): Settings {
   // `set`, so only write when something actually changed — otherwise this churns
   // the settings file on every read. (audit P1)
   const cur = s.store
-  // outputDir is intentionally left blank by default — an empty value routes each
-  // download into Documents\Video / Documents\Audio by kind (see buildCommand).
-  // Only an explicit user choice (Settings → Download folder) overrides that.
+  // videoDir/audioDir are intentionally left blank by default — an empty value
+  // routes that kind into Documents\Video / Documents\Audio (see buildCommand).
+  // Only an explicit user choice (Settings → folders) overrides that.
   // Migrate settings files that predate downloadOptions (or hold a partial one),
   // but only persist when sanitizing actually altered the stored value.
   const sanitized = sanitizeOptions(cur.downloadOptions)
@@ -212,8 +215,13 @@ export function setSettings(partial: Partial<Settings>): Settings {
         // group (it merges field changes locally before calling setSettings).
         s.set('downloadOptions', sanitizeOptions(value))
         break
-      case 'outputDir':
-        if (typeof value === 'string' && isSafeOutputDir(value.trim())) s.set('outputDir', value.trim())
+      case 'videoDir':
+      case 'audioDir':
+        // An empty string is allowed — it clears the override and restores the
+        // Documents\Video / Documents\Audio default for that kind.
+        if (typeof value === 'string' && (value.trim() === '' || isSafeOutputDir(value.trim()))) {
+          s.set(key, value.trim())
+        }
         break
       case 'filenameTemplate':
         if (typeof value === 'string' && isSafeFilenameTemplate(value.trim())) {