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/main/download.ts

@@ -209,7 +209,9 @@ export function buildCommand(opts: StartDownloadOptions, cookiesFile?: string):
         outDir,
         opts.collection,
         '%(title)s.%(ext)s',
-        settings.collectionOutputTemplate
+        // A per-download override (a Media Profile's outputTemplate) wins over the
+        // global collection-layout setting.
+        opts.collectionOutputTemplate ?? settings.collectionOutputTemplate
       )
     : join(outDir, filenameTemplate)
   // Per-download override wins; otherwise use the persisted defaults.