fix(plugins): address review feedback for Matrix recovery paths (#52899)

1. Narrow loadConfigForInstall() to catch only INVALID_CONFIG errors,
   letting real failures (fs permission, OOM) propagate.
2. Assert allow array is properly cleaned in stale-cleanup test.
3. Add comment clarifying version-resolution is already addressed via
   the shared VERSION constant.
4. Run cleanStaleMatrixPluginConfig() during install so
   persistPluginInstall() → writeConfigFile() does not fail validation
   on stale Matrix load paths.

src/commands/doctor/providers/matrix.test.ts

@@ -170,6 +170,8 @@ describe("doctor matrix provider helpers", () => {
     // Config should have stale refs removed
     expect(result.config.plugins?.installs?.matrix).toBeUndefined();
     expect(result.config.plugins?.load?.paths).toEqual(["/other/path"]);
+    // Allowlist should have matrix removed but keep other entries
+    expect(result.config.plugins?.allow).toEqual(["other-plugin"]);
   });
 
   it("returns no changes when Matrix install path exists", async () => {