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/App.tsx

@@ -4,6 +4,7 @@ import Header from "./components/Header";
 import RenamePanel from "./components/RenamePanel";
 import EpisodesPanel from "./components/EpisodesPanel";
 import SubtitlesPanel from "./components/SubtitlesPanel";
+import SfvPanel from "./components/SfvPanel";
 import PanelStub from "./components/PanelStub";
 
 export default function App() {
@@ -22,6 +23,8 @@ export default function App() {
             <EpisodesPanel />
           ) : selected === "subtitles" ? (
             <SubtitlesPanel />
+          ) : selected === "sfv" ? (
+            <SfvPanel />
           ) : (
             <PanelStub name={current.name} />
           )}