Add Autodesk cloud sync connector

Initial implementation of the ifcviewer-autodesk connector — a separate process that bridges the IfcViewer to Autodesk APS (BIM 360 / ACC). Speaks JSON-RPC 2.0 over stdio per CLOUD_SYNC_PROTOCOL.md (also added). PKCE OAuth with keyring-backed token storage, customtkinter browse/picker UI, and PyInstaller packaging.

Implements both interactive and non-interactive variants of each push/pull (pull_ifcfed[_interactive], pull_models[_interactive], push_ifcfed[_interactive], push_model[_interactive]) so the viewer can offer both "Save"/"Open from Cloud" and "Save As"/"Add Model from Cloud" entry points. File transfers report progress through a dialog with per-byte updates; pull_models shows "(i/N)" for batches.

Generated with the assistance of an AI coding tool.

src/ifcviewer-autodesk/connector.json

@@ -0,0 +1,6 @@
+{
+  "id": "autodesk",
+  "name": "Autodesk Forma",
+  "version": "0.1.0",
+  "exec": "ifcviewer-autodesk"
+}