fix: replace 'Index error' with graceful handling on fresh installs

Separate 'unavailable' (qmd not installed) from 'error' (indexing failed)
phases. Unavailable state is hidden from the status bar instead of showing
a persistent orange error. Actual errors show "Index failed — retry" with
click-to-retry. Both phases auto-dismiss after a timeout.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -391,11 +391,11 @@ async fn start_indexing(app_handle: tauri::AppHandle, vault_path: String) -> Res
             match indexing::auto_install_qmd() {
                 Ok(_) => log::info!("qmd auto-installed successfully"),
                 Err(e) => {
-                    log::warn!("qmd auto-install failed: {e}");
+                    log::info!("qmd not available (search disabled): {e}");
                     let _ = app_handle.emit(
                         "indexing-progress",
                         IndexingProgress {
-                            phase: "error".to_string(),
+                            phase: "unavailable".to_string(),
                             current: 0,
                             total: 0,
                             done: true,