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/adapters/exif/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "adapters-exif"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+domain   = { workspace = true }
+bytes    = { workspace = true }
+nom-exif = { version = "2.5", features = ["serde"] }