[upload] Auto-unlock storage in the upload modal for a kept-unlocked session (#51)

The upload modal only READ storage's unlock state (isUnlocked) on load/open/refresh
— it never auto-unlocked the way the profile Storage pane does. So after a refresh
with "keep unlocked" ticked, the upload modal still opened with storage Locked even
though the signer had been restored.

Add UploadModal.maybeAutoUnlockStorage(pubkey), called on load(), open(), and
refreshState(): if storage is locked but a decrypt-capable signer is already present
(e.g. a kept-unlocked nsec restored on refresh), unlock silently. Guarded two ways:
  - only when the account ALREADY exists (new storageService.hasStoredAccount) so it
    never auto-creates storage for magnet/URL-only uploaders, and
  - only when the signer is already available, so it never triggers a fresh
    permission prompt on modal open.

Tests: storageService.hasStoredAccount (false before setup, true after unlock,
never creates an account, survives lock). Lint + build green.

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

tests/storage-service.test.mjs

@@ -277,4 +277,29 @@ describe("StorageService", () => {
       /Storage is locked/,
     );
   });
+
+  // hasStoredAccount lets the upload modal auto-unlock EXISTING storage on refresh
+  // without unlock() creating a fresh account for users who never set it up (#51).
+  test("hasStoredAccount() is false before setup, true after, and never creates an account", async () => {
+    assert.strictEqual(
+      await storageService.hasStoredAccount(pubkey),
+      false,
+      "no account before any unlock",
+    );
+    // A read-only existence check must not create an account.
+    assert.strictEqual(await storageService.hasStoredAccount(pubkey), false);
+
+    await storageService.unlock(pubkey, { signer: mockSigner });
+    assert.strictEqual(
+      await storageService.hasStoredAccount(pubkey),
+      true,
+      "account exists after unlock persisted the encrypted master key",
+    );
+
+    // Survives a lock (existence is on-disk, not the in-memory master key).
+    storageService.lock(pubkey);
+    assert.strictEqual(await storageService.hasStoredAccount(pubkey), true);
+
+    assert.strictEqual(await storageService.hasStoredAccount(""), false);
+  });
 });