feat(notifications): add overlay notifications with position config

- Add Catppuccin Macchiato overlay notification stack with 3s transient timeout
- Add `notifications.overlayPosition` config (top-left | top | top-right)
- Route startup tokenization and subtitle annotation status through configured surfaces
- Deduplicate rapid subtitle mode toggle notifications
- Change `both` to mean overlay + system; add `osd-system` as legacy alias for old behavior
- Keep `osd`/`osd-system` as config-file-only legacy values; Settings UI offers overlay/system/both/none

src/shared/subminer-plugin-script-opts.ts

@@ -10,6 +10,7 @@ export interface SubminerPluginRuntimeScriptOptConfig {
   autoStart: boolean;
   autoStartVisibleOverlay: boolean;
   autoStartPauseUntilReady: boolean;
+  osdMessages: boolean;
   texthookerEnabled: boolean;
   aniskipEnabled: boolean;
   aniskipButtonKey: string;
@@ -44,6 +45,7 @@ export function buildSubminerPluginRuntimeScriptOptParts(
     `subminer-auto_start_pause_until_ready=${boolScriptOpt(
       runtimeConfig.autoStartPauseUntilReady,
     )}`,
+    `subminer-osd_messages=${boolScriptOpt(runtimeConfig.osdMessages)}`,
     `subminer-texthooker_enabled=${boolScriptOpt(runtimeConfig.texthookerEnabled)}`,
     `subminer-aniskip_enabled=${boolScriptOpt(runtimeConfig.aniskipEnabled)}`,
     `subminer-aniskip_button_key=${aniskipButtonKey}`,