fix(mcp-server): do not store source audio path as STT gallery file

STT does not produce a local media file, so journal.filePath should be
null. Otherwise admin gallery tries to serve the source file from outside
the media dir and gets a broken link.

NexusAI/packages/mcp-server/src/handlers.ts

@@ -162,7 +162,8 @@ export class Handlers {
         inputSummary: summarize({ ...args.input, audioBase64: args.input.audioBase64 ? '[base64]' : undefined }),
         status: 'done',
         costUsd: 0,
-        filePath: args.input.audioPath ?? null,
+        // STT does not produce a local media file; the source audio path stays in inputSummary.
+        filePath: null,
         resultUrl: null,
         error: null,
         durationMs: Date.now() - started,