build: root .cargo/config.toml enables the real OCIO bridge workspace-wide

cargo test from the workspace root does not read
crates/oakcommon/.cargo/config.toml, so ocio-sys silently built its
stub bridge and oakcommon's OCIO tests failed with empty configs.
Mirror the same env (OCIO_RS_ENABLE_REAL/OCIO_INSTALL_DIR/OCIO_RS_LINK)
at the root; no manual environment variables are needed any more.

.cargo/config.toml

@@ -0,0 +1,31 @@
+# Oak Video Editor - Non-Linear Video Editor
+# Copyright (C) 2026 Oak Team
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# `ocio-sys` (the FFI layer behind `ocio-rs`) does not probe the system for
+# OpenColorIO on its own: with no configuration it builds a *stub* bridge
+# whose calls all fail. These environment variables make it link the real
+# Homebrew OpenColorIO dylib:
+#
+#   OCIO_RS_ENABLE_REAL  - opt into the real (non-stub) bridge
+#   OCIO_INSTALL_DIR     - prefix whose include/ and lib/ hold OpenColorIO
+#   OCIO_RS_LINK         - Homebrew ships a dylib, so link dynamically
+#
+# See README.md "Build & test" for the bundled alternative.
+
+[env]
+OCIO_RS_ENABLE_REAL = "1"
+OCIO_INSTALL_DIR = "/opt/homebrew/opt/opencolorio"
+OCIO_RS_LINK = "dynamic"