fix(auth): address PR #757 review feedback

- Branch the ProvisioningRequiredError message on the elicit result so a
  user who acknowledged the prompt isn't told to call
  nc_auth_provision_access (which would loop an LLM that just confirmed
  via elicitation). Other paths keep the existing instruction.
- Convert present_login_url's f-string logger.warning to lazy %s, matching
  present_provisioning_required and the repo's lazy-logging preference.
- Add a test for NEXTCLOUD_PUBLIC_ISSUER_URL trailing-slash normalization.
- Strengthen the decorator-elicits test: split into the "accepted" and
  "message_only" branches so the error-message change is regression-tested.

Refs: cbcoutinho/nextcloud-mcp-server#757#issuecomment-4363552487

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/test_elicitation.py

@@ -31,6 +31,15 @@ def test_astrolabe_settings_url_prefers_public_issuer(monkeypatch):
     )
 
 
+def test_astrolabe_settings_url_strips_trailing_slash_from_public_issuer(monkeypatch):
+    """Trailing slash on NEXTCLOUD_PUBLIC_ISSUER_URL is normalized."""
+    monkeypatch.setenv("NEXTCLOUD_PUBLIC_ISSUER_URL", "https://nc.example.com/")
+
+    assert (
+        _astrolabe_settings_url() == f"https://nc.example.com{ASTROLABE_SETTINGS_PATH}"
+    )
+
+
 def test_astrolabe_settings_url_falls_back_to_host(monkeypatch):
     """When only NEXTCLOUD_HOST is set, use it (and strip a trailing slash)."""
     monkeypatch.setenv("NEXTCLOUD_HOST", "https://only-host.example.com/")