feat(rust): first green Rust crates — oakcore-rs, oakundo, oakcommon, oaktimeline, oakaudio

- oakcore-rs: Rational/TimeRange/TimeRangeList/PixelFormat/SampleFormat
  mirroring oakcore C++ semantics (91.6% coverage)
- oakundo: UndoCommand/UndoStack with vtable commands (99.6%)
- oakcommon: config/XML/VideoParams/logging etc. (89.8%, 516 tests);
  XML via quick-xml, logging via the log facade
- oaktimeline: markers/workarea/edit commands (95.4%)
- oakaudio: processor/manager/sync/waveform/levelmeter (88.4%)
- unified -MMCCCC error codes across all C ABI headers (registry in
  include/common/error.h; pass-through rule)
- olive::Variant moved node -> common (cross-module value type)
- oakcommon_videoparams_set_is_3d added to the C ABI
- M11 (oakplugin Rust rewrite) plan + notes.md freeze line for the
  inter-module C ABI wiring

include/codec/error.h

@@ -30,12 +30,12 @@
  * (including the terminating NUL) as a non-negative value instead.
  */
 #define OAKCODEC_OK 0 /**< Success. */
-#define OAKCODEC_E_INVALID (-1) /**< NULL handle or invalid argument. */
-#define OAKCODEC_E_STATE (-2) /**< Call not valid in the current state. */
-#define OAKCODEC_E_FAILED (-3) /**< The underlying operation failed. */
-#define OAKCODEC_E_NOT_FOUND (-4) /**< Index out of range / entry not found. */
-#define OAKCODEC_E_NOMEM (-5) /**< Allocation failed. */
-#define OAKCODEC_E_CANCELLED (-6) /**< The operation was cancelled. */
+#define OAKCODEC_E_INVALID (-50001) /**< NULL handle or invalid argument. */
+#define OAKCODEC_E_STATE (-50002) /**< Call not valid in the current state. */
+#define OAKCODEC_E_FAILED (-50003) /**< The underlying operation failed. */
+#define OAKCODEC_E_NOT_FOUND (-50004) /**< Index out of range / entry not found. */
+#define OAKCODEC_E_NOMEM (-50005) /**< Allocation failed. */
+#define OAKCODEC_E_CANCELLED (-50006) /**< The operation was cancelled. */
 
 /**
  * @brief Current ABI version stamped into every oakcodec handle.