fix: clarify saved upload completion UI

The previous page showed a static "Server online" pill even though it did not
track backend liveness. It also left the selected file in an uploadable state
after completion, which made it too easy to start the same file again and then
land in a saved record that could only fail with "complete file already
exists".

Remove the misleading server-status UI and make saved uploads describe their
next action. Records with every chunk uploaded now show a Finish action, stale
server records are cleared, and a terminal "complete file already exists"
response clears the saved browser progress instead of inviting another resume.
A successful completion also clears the active file selection so the primary
actions settle back to idle.

Test Plan:
- just check

Refs: none

tests/static_server.rs

@@ -23,7 +23,8 @@ async fn serves_index_page() -> Result<(), Box<dyn std::error::Error>> {
 
     assert!(body.contains("<title>upl</title>"));
     assert!(body.contains("Choose file"));
-    assert!(body.contains("Pending uploads"));
+    assert!(body.contains("Saved upload progress"));
+    assert!(!body.contains("Server online"));
 
     Ok(())
 }