feat: real EXIF extraction via adapters-exif crate

- MetadataExtractorPort in domain (bytes → StructuredData)
- adapters-exif: NomExifExtractor using nom-exif, handles EXIF + TrackInfo
- Worker's MetadataExtractorPlugin delegates to port, no longer knows nom-exif
- Filters noisy binary tags (U8Array, Undefined, Unknown)

crates/worker/Cargo.toml

@@ -15,6 +15,7 @@ adapters-postgres  = { path = "../adapters/postgres" }
 adapters-storage   = { workspace = true }
 adapters-nats      = { workspace = true }
 event-transport    = { workspace = true }
+adapters-exif      = { workspace = true }
 async-nats         = { workspace = true }
 
 futures           = { workspace = true }