[ui] upload modal: prompt for the nsec passphrase instead of dead-ending after reload

With a persisted ("remember this key") nsec login, uploading a video after a page
reload reported "storage is locked" and then "No signer available to unlock storage."
The reload restores the logged-in pubkey but NOT the in-memory signer (the key is
passphrase-encrypted), and UploadModal.handleUnlock dead-ended on the alert — it never
asked for the passphrase.

Fix (mirrors the storage pane's #36 behavior): handleUnlock now calls
promptStoredNsecUnlock(pubkey) when there's no usable signer. If the active account has
a locked saved nsec key (getStoredSessionActorMetadata), it shows an actionable message
and opens the login modal's existing unlock-saved-key (passphrase) flow via a new
onRequestUnlock hook (wired in initUploadModal -> app.loginModalController.openModal),
instead of the dead-end alert. After the user re-enters their passphrase the signer is
active and the upload proceeds.

Tests: tests/upload-modal-nsec-unlock.test.mjs (5 — detects locked nsec for the active
account + opens unlock; ignores missing/non-nsec/other-account; falls through with no
hook). Build + lint clean.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/ui/initUploadModal.js

@@ -55,6 +55,22 @@ export function initUploadModal({
           app.profileController.show("storage");
         }
       },
+      // Open the login modal's unlock-saved-key (passphrase) flow when a persisted
+      // nsec session is locked after a reload.
+      onRequestUnlock: () => {
+        try {
+          if (typeof app?.initializeLoginModalController === "function") {
+            app.initializeLoginModalController();
+          }
+          const controller = app?.loginModalController;
+          if (controller && typeof controller.openModal === "function") {
+            return controller.openModal({}) !== false;
+          }
+        } catch (error) {
+          /* best-effort */
+        }
+        return false;
+      },
     });
 
   const boundSubmitHandler =