feat: real XMP sidecar adapter, replaces LogSidecarWriter stubs

- adapters-sidecar: XmpSidecarWriter using xmp_toolkit
- Writes StructuredData → XMP with EXIF/DC/XMP namespace routing
- Reads XMP back to StructuredData
- Wired into bootstrap + worker, deleted both LogSidecarWriter stubs

crates/bootstrap/Cargo.toml

@@ -13,6 +13,7 @@ application     = { workspace = true }
 adapters-auth   = { workspace = true }
 
 adapters-storage   = { workspace = true, features = ["s3"] }
+adapters-sidecar   = { workspace = true }
 adapters-nats      = { workspace = true }
 adapters-event-transport = { workspace = true }
 async-nats         = { workspace = true }