feat: Make tagging photos work

Stop deriving tags from filename, read/write tags stored in Firestore. Maybe keep the filename tags if they're chill, maybe just parse better? idfk really.

Find where photo tagging is currently inferred from filenames and where photo metadata is saved/read from Firestore. Trace the photo upload/edit flow first to identify the exact path that assigns tags. Then update that flow so tags come from Firestore records (or include filename fallback if decided) and persist accordingly. Run the photo feature tests or end-to-end upload flow to verify tags are read/written from Firestore as expected.

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