feat(explore): carry the local row id on a top result

`TopResult` was the one projection here that shipped `inLibrary` and no
local id, so the top-results cards had no choice but to read the weaker
flag. Every sibling model — `MBArtist`, `MBReleaseGroup`, `MBRecording`
— already carries `LocalID`, and the candidate builders had the value
in hand at every construction site.

`LocalID` is set and cleared by a test against `audio_files`, so it
means "there is something of mine here". `InLibrary` is written by the
same pass but is a one-way ratchet the prune can only clear alongside a
local id; it stays for scoring, which is where an approximate answer is
fine.

frontend/bindings/yellowjacket/backend/explore/models.ts

@@ -431,8 +431,17 @@ export interface TopResult {
 
     /**
      * Library status — populated from index cross-reference columns.
+     * 
+     * LocalID is the one the cards read.  It is the local row behind
+     * this entity — an album, a file, an artist — and it is set and
+     * cleared by a test against `audio_files`, so it means "there is
+     * something of mine here".  InLibrary is written by the same pass
+     * but is a one-way ratchet the prune can only clear alongside a
+     * local id, so it is the weaker of the two and stays for scoring
+     * (`fwInLibrary`), which is where an approximate answer is fine.
      */
     "inLibrary": boolean;
+    "localId"?: number;
 }
 
 /**