Downloaded Models Are Missing from the Downloads Section, Causing Duplicate Downloads  #132

When I select and download a model for the first time during the initial app setup, the model appears to download successfully. However, after navigating to the Downloads or model management section, the same model is not displayed as downloaded.

If I tap the model again, the app starts downloading the same model a second time, potentially wasting storage space, bandwidth, and time.

Steps to Reproduce

1. Install and open AnythingLLM Mobile.
2. Select a local model during the initial setup.
3. Wait until the model download completes successfully.
4. Open the Downloads or model management section.
5. Check whether the downloaded model is listed.
6. Select the same model again.

Actual Behavior
The previously downloaded model is not correctly reflected in the download management UI, and selecting it again triggers another download.

Expected Behavior
The app should maintain a consistent model registry and accurately display download status. Existing model files should be detected, and duplicate downloads should be prevented.

Suggested Fix
Synchronize download state with persistent model metadata and on-disk files. Add duplicate-download protection and validate model integrity before starting a new download.

Device Model: OPPO CPH2269
Brand: OPPO
Operating System: Android 12
Device Platform: MediaTek MT6765
CPU Architecture: ARM64 (aarch64)
RAM: Approximately 4 GB
Available Storage: Depends on current usage
Device Type: Android smartphone