fix(playback): keep the saved Embedded MPV player when the mpv check is inconclusive

On Linux native-view the support check runs `mpv --version` by bare name
and waits for the login shell PATH first. Since #1784 that lookup is
asynchronous with a 10 s budget; when it ran out, the check ran on the
inherited PATH and answered a plain `supported: false`. The settings store
took that as a verdict and persisted the default player over a saved
Embedded MPV selection. The main process probed again once the shell
answered, but nothing restored the setting.

`EmbeddedMpvSupport` now carries `inconclusive`. The native service sets it
on a missing mpv while its probe has only seen the inherited PATH; the IPC
handler declares that state before probing and registers the re-probe
before the check, so a throwing check cannot leave it stuck. Every other
answer stays final.

Consumers no longer settle on an inconclusive answer: the settings store
keeps the saved player, and the command palette and the settings search
probe again on their next use instead of caching it for the session.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

libs/shared/interfaces/src/lib/embedded-mpv-session.interface.ts

@@ -39,6 +39,13 @@ export interface EmbeddedMpvSupport {
     supported: boolean;
     platform: string;
     reason?: string;
+    /**
+     * True when `supported: false` is not a verdict on this machine yet: the
+     * Linux native-view `mpv` executable was looked up before the login shell
+     * PATH arrived, and is looked up again once the shell answers. Never
+     * persist a decision made from such an answer; ask again later.
+     */
+    inconclusive?: boolean;
     capabilities?: EmbeddedMpvCapabilities;
     /**
      * Rendering engine the main process will use for new sessions.