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/src/services/sidecar.rs

@@ -9,13 +9,12 @@ use application::sidecar::{
 };
 use presentation::state::SidecarHandlers;
 
-use crate::log_sidecar_writer::LogSidecarWriter;
-
 pub fn build(pool: &PgPool) -> SidecarHandlers {
     let metadata_repo = Arc::new(PostgresAssetMetadataRepository::new(pool.clone()));
     let asset_repo = Arc::new(PostgresAssetRepository::new(pool.clone()));
     let sidecar_repo = Arc::new(PostgresSidecarRepository::new(pool.clone()));
-    let sidecar_writer: Arc<LogSidecarWriter> = Arc::new(LogSidecarWriter);
+    let sidecar_writer: Arc<adapters_sidecar::XmpSidecarWriter> =
+        Arc::new(adapters_sidecar::XmpSidecarWriter);
 
     let export = Arc::new(ExportSidecarHandler::new(
         metadata_repo.clone(),