Add SFV panel: compute/verify CRC32/MD5/SHA1 checksums, .sfv/.md5/.sha1 sidecar files

Fully local feature - no network access, no credentials. New aurora-curator-core::sfv
module streams file hashing in 64KB chunks and handles both the traditional .sfv
format (CRC32, "name checksum" layout) and the GNU coreutils md5sum/sha1sum sidecar
convention (.md5/.sha1, "checksum  name" layout), dispatched on a shared ChecksumKind
enum. New src-tauri/src/sfv.rs wraps it in three Tauri commands - compute_checksums
(per-file error isolation), save_checksum_file (native Save dialog), and
verify_checksum_file (resolves each entry against the checksum file's own parent
directory, reports OK/Mismatch/Missing per entry). New SfvPanel.tsx/.css wires it all
into the sidebar's SFV screen - load files, pick a checksum type, Compute, Save, or
Verify against an existing checksum file.

14 new core-crate tests + 1 new src-tauri test, all passing (workspace: 160/160).
Verified end-to-end with a 22-check Playwright script against npm run dev.

src-tauri/src/lib.rs

@@ -5,6 +5,7 @@ mod history;
 mod metadata;
 mod presets;
 mod settings;
+mod sfv;
 mod subtitles;
 
 use aurora_curator_core::format::ExpressionFormat;
@@ -117,6 +118,9 @@ pub fn run() {
             subtitles::search_subtitles,
             subtitles::download_subtitle,
             episodes::browse_episodes,
+            sfv::compute_checksums,
+            sfv::save_checksum_file,
+            sfv::verify_checksum_file,
             history::list_rename_history,
             history::undo_rename_batch,
             presets::list_presets,