Unlinking a device is one flow in the core: link::unlink

The desktop's sync_unlink and the ffi's unlink were both written out in full: try
the revoke, clear the link either way, and log the outcome. link::unlink(db, held)
now does that. Each client reads its link with state::credentials (with its seal)
before the await and passes it in.

DRY pass #2, batch 1, F3 (#5372).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

desktop/src-tauri/src/commands/sync.rs

@@ -121,21 +121,12 @@ pub struct UnlinkResult {
 /// honestly, and the link cleared either way.
 #[tauri::command]
 pub async fn sync_unlink(db: State<'_, Db>) -> Result<UnlinkResult, String> {
-    // Read and release before the network call: a std MutexGuard isn't Send, and
-    // holding the store across a round-trip would freeze every note operation in
-    // the UI.
-    let link = {
+    let held = {
         let conn = db.conn()?;
         state::credentials(&conn, None).map_err(|e| e.to_string())?
     };
-    let revoked = match &link {
-        Some((base_url, token)) => client::revoke_self(base_url, token).await,
-        None => client::RevokeOutcome::Skipped,
-    };
-
+    let revoked = link::unlink(&db, held).await?;
     let conn = db.conn()?;
-    state::clear_link(&conn).map_err(|e| e.to_string())?;
-    log::info!("unlinked from server (server-side token: {revoked:?})");
     Ok(UnlinkResult {
         status: state::status(&conn).map_err(|e| e.to_string())?,
         revoked,