Fix Git Sync wiping the entire repo when a fresh clone's DB is empty

exportAllConversations()'s orphan-cleanup treated "zero local
conversations" as "every synced conversation was deleted," so a
just-cloned repo on a new machine could get emptied and pushed before
the post-clone import ever ran. orphanedExportFilenames() now returns
no orphans when the local ID set is empty, and cloneRepository()
imports immediately after cloning to close the window entirely.

oAI/Services/GitSyncService.swift

@@ -68,6 +68,11 @@ class GitSyncService {
         _ = try await runGit(["clone", url, localPath])
         syncStatus.isCloned = true
 
+        // Import immediately so this machine's DB is never left empty after a clone —
+        // an empty DB is what makes the next export think every existing conversation
+        // was deleted (see exportAllConversations's orphan-cleanup guard).
+        _ = try? await importAllConversations()
+
         await updateStatus()
     }
 
@@ -202,7 +207,15 @@ class GitSyncService {
         currentIds: Set<String>,
         files: [(filename: String, markdown: String)]
     ) -> [String] {
-        files.compactMap { file in
+        // A locally-empty conversation list is indistinguishable here from "nothing has been
+        // imported into this machine's DB yet" (e.g. right after a fresh clone). Treating it as
+        // "every existing file was deleted" wiped a user's entire sync repo in production: clone
+        // completed, an auto-sync fired before the post-clone import finished, every synced
+        // conversation looked orphaned, and the deletion got committed and pushed. Skipping
+        // cleanup here means a genuine last-conversation deletion won't propagate until another
+        // conversation exists locally — a far smaller cost than mass data loss.
+        guard !currentIds.isEmpty else { return [] }
+        return files.compactMap { file in
             guard let export = try? ConversationExport.fromMarkdown(file.markdown) else { return nil }
             return currentIds.contains(export.id) ? nil : file.filename
         }