Bugfix: Indexing won't start on fresh DB

(Caused by our recent changes)

`resume_or_scan()` set `scanning = true` early to suppress the verifier during startup, but `start_scan()` then rejected with "Scan already running" because its guard checks the same flag before setting it.

- Move the early `scanning = true` from `resume_or_scan()` into `start_replay()` — the only path that doesn't go through `start_scan()`
- `start_scan()` still sets the flag itself, so both paths are covered
- The fallback-from-replay and manual-start paths work correctly because `scanning` is `false` when they call `start_scan()`

Author: vdavid

apps/desktop/src-tauri/src/indexing/mod.rs

@@ -266,11 +266,6 @@ impl IndexManager {
     ///
     /// **No existing index:** Full scan via `start_scan()`.
     pub fn resume_or_scan(&mut self) -> Result<(), String> {
-        // Suppress verifier and other concurrent reads until replay/scan completes.
-        // start_scan() sets this again (harmless), and both scan and replay
-        // completion paths reset it to false.
-        self.scanning.store(true, Ordering::Relaxed);
-
         let status = self
             .store
             .get_index_status()
@@ -379,6 +374,10 @@ impl IndexManager {
             None
         };
 
+        // Suppress verifier until replay completes. The spawned task resets
+        // this to false when replay is done (or on fallback to full scan).
+        self.scanning.store(true, Ordering::Relaxed);
+
         // Spawn the replay event processing loop
         let writer = self.writer.clone();
         let app = self.app.clone();