fix(dropbox): fix Invalid redirect_uri error by adding PUBLIC_BASE_URL config and URL-encoding

- Add PUBLIC_BASE_URL optional config to override auto-detected OAuth redirect URIs
  when behind a reverse proxy that doesn't forward X-Forwarded-Proto headers
- Add _build_dropbox_redirect_uri() helper in app/api/dropbox.py
- URL-encode redirect_uri in server-side Dropbox authorization URL
- Add _get_dropbox_callback_url() helper in app/views/dropbox.py
- Pass callback_url to both setup and callback templates
- Update templates to use server-provided callback_url instead of window.location.origin
- Update settings_service.py to register new setting
- Update .env.demo, ConfigurationGuide.md, and DropboxSetup.md documentation
- Add tests for new helper functions and global-authorize-url endpoint

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

tests/test_views_dropbox.py

@@ -144,3 +144,37 @@ class TestDropboxViews:
         assert response.status_code == 200
         assert b"/Documents/Uploads" in response.content
         assert b"Back to Integrations" in response.content
+
+
+@pytest.mark.integration
+class TestDropboxCallbackUrl:
+    """Tests that the callback_url is correctly passed to templates."""
+
+    def test_setup_page_includes_callback_url(self, client):
+        """Setup page should include the callback_url variable in its response."""
+        response = client.get("/dropbox-setup")
+        assert response.status_code == 200
+        # callback_url is embedded in the JS as the dropboxCallbackUrl constant
+        assert b"dropboxCallbackUrl" in response.content
+
+    def test_callback_page_includes_callback_url(self, client):
+        """Callback page should embed the server-side callback URL."""
+        response = client.get("/dropbox-callback?code=testcode")
+        assert response.status_code == 200
+        # callback_url is used as the redirectUri
+        assert b"redirectUri" in response.content
+
+    def test_setup_page_uses_public_base_url_when_set(self, client):
+        """When PUBLIC_BASE_URL is configured, it should appear in the redirect URI hint."""
+        with patch("app.views.dropbox.settings") as mock_settings:
+            mock_settings.public_base_url = "https://configured.example.com"
+            mock_settings.dropbox_app_key = ""
+            mock_settings.dropbox_app_secret = ""
+            mock_settings.dropbox_refresh_token = ""
+            mock_settings.dropbox_folder = ""
+            mock_settings.dropbox_allow_global_credentials_for_integrations = False
+            response = client.get("/dropbox-setup")
+        assert response.status_code == 200
+        # The configured public_base_url hostname must appear in the page (redirect URI display)
+        page_text = response.text
+        assert "configured.example.com/dropbox-callback" in page_text