BUG: Face clusters show fewer photos than face search for the same person

### Is there an existing issue for this?

- [x] I have searched the existing issues

### What happened?

## What happened?
After AI tagging completes, Face Collections (People view) show very few photos for a person,
while face search returns many more photos for the same person.

Example from my local setup:
- AI Tagging → Face Collections → Person 5eb9 shows **3 photos**
- Home → Face search using the same person returns **13 photos**

This is confusing from a user perspective since both features appear to answer the same question:
"Show me all photos of this person."

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## How to reproduce
1. Add a folder with many photos of the same person
2. Enable AI tagging and wait for it to complete
3. Go to AI Tagging → Face Collections
4. Click a person cluster and note the photo count
5. Use Home search with a photo of the same person
6. Observe that search returns significantly more photos than the cluster view

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## Expected behaviour
Face Collections and face search should be consistent, or the UI should clearly explain
why results differ.

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## Actual behaviour
Face Collections show only a small subset of photos, while face search returns many more
for the same person.

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## Technical analysis (initial one)
From tracing the backend pipeline:
- Face clustering uses DBSCAN with stricter similarity thresholds and may exclude faces as noise
- Face search compares raw embeddings with a looser threshold and ignores clusters entirely
- Some faces remain unclustered but still appear in search results

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