feat(pinchflat): Media Profiles — named download presets per Library source

A MediaProfile bundles { kind, quality, options, outputTemplate, extraArgs }
that a Source points at via Source.profileId, overriding the global defaults
field-by-field for that source's downloads.

Backend mirrors CommandTemplate: profiles.ts (createJsonStore, PROFILES_MAX,
isProfileLike + sanitize), CRUD IPC (profiles:list/save/remove) + preload +
useProfiles store; Source.profileId + sources:set-profile. Pure resolution
in @shared/profileResolve.ts (profile → global, per field; unit-tested).
Applied in the sources-store enqueueItems; a per-download collectionOutput-
Template override threads to buildArgs so a profile's outputTemplate wins.

UI: ProfileManager (mirrors TemplateManager) in a new Settings → Advanced →
Media profiles card, plus a per-source Profile picker in the Library source
detail. Both live-verified in the preview; 354 tests pass.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/preload/index.ts

@@ -18,6 +18,7 @@ import {
   type CookiesStatus,
   type CookiesLoginResult,
   type CommandTemplate,
+  type MediaProfile,
   type CommandPreviewResult,
   type ErrorLogEntry,
   type BackupExportResult,
@@ -126,6 +127,14 @@ const api = {
   removeTemplate: (id: string): Promise<CommandTemplate[]> =>
     ipcRenderer.invoke(IpcChannels.templatesRemove, id),
 
+  listProfiles: (): Promise<MediaProfile[]> => ipcRenderer.invoke(IpcChannels.profilesList),
+
+  saveProfile: (profile: MediaProfile): Promise<MediaProfile[]> =>
+    ipcRenderer.invoke(IpcChannels.profilesSave, profile),
+
+  removeProfile: (id: string): Promise<MediaProfile[]> =>
+    ipcRenderer.invoke(IpcChannels.profilesRemove, id),
+
   /** Build the exact yt-dlp command line for the given form state, without running it. */
   previewCommand: (opts: StartDownloadOptions): Promise<CommandPreviewResult> =>
     ipcRenderer.invoke(IpcChannels.commandPreview, opts),
@@ -214,6 +223,10 @@ const api = {
   setSourceWatched: (id: string, watched: boolean): Promise<Source[]> =>
     ipcRenderer.invoke(IpcChannels.sourceSetWatched, id, watched),
 
+  /** Point a source at a MediaProfile, or clear it (profileId = null). */
+  setSourceProfile: (id: string, profileId: string | null): Promise<Source[]> =>
+    ipcRenderer.invoke(IpcChannels.sourceSetProfile, id, profileId),
+
   /** Re-index all watched sources; resolves with the videos found new. Named to
    *  match the main function `syncWatchedSources` (L92). */
   syncWatchedSources: (): Promise<SyncResult> => ipcRenderer.invoke(IpcChannels.sourcesSync),