feat(overlay): add loading OSD spinner and queue notifications until ren

- Show mpv OSD spinner from start-file until subminer-overlay-loading-ready; force-shown for visible-overlay startup regardless of osd_messages setting
- Gate non-macOS overlay visibility on content-ready so first subtitle line is immediately hoverable and clickable
- Queue startup notifications in main process until overlay window finishes loading; upsert progress cards by id to avoid cold-start floods
- Defer background warmups until after overlay runtime init so queued notifications can deliver promptly
- Preserve character dictionary checking/building/importing/ready phases as distinct history entries; route building and importing to system notifications when notificationType is both

launcher/config-domain-parsers.test.ts

@@ -207,6 +207,7 @@ test('buildPluginRuntimeScriptOptParts emits config values that override plugin
       'subminer-backend=x11',
       'subminer-auto_start=yes',
       'subminer-auto_start_visible_overlay=no',
+      'subminer-overlay_loading_osd=no',
       'subminer-auto_start_pause_until_ready=yes',
       'subminer-auto_start_pause_until_ready_timeout_seconds=30',
       'subminer-osd_messages=yes',
@@ -240,6 +241,7 @@ test('buildPluginRuntimeScriptOptParts strips script-option delimiters from stri
       'subminer-backend=x11',
       'subminer-auto_start=yes',
       'subminer-auto_start_visible_overlay=no',
+      'subminer-overlay_loading_osd=no',
       'subminer-auto_start_pause_until_ready=yes',
       'subminer-auto_start_pause_until_ready_timeout_seconds=30',
       'subminer-osd_messages=no',