core: merge oak-common into oak-core

oak-common is gone; its modules (configstore, xmlutils, ocioutils,
oiioutils, colormath, colortransform, videoparams, ffmpegutils, ...)
now live in oak-core alongside the value types. The render value/GPU
types moved too: backend (wgpu context + DisplayRenderer), color
(ColorProcessor over ocio-rs), texture, frame, and the commonutil
config helpers.

Fix-ups to make the merged tree build and pass tests:

- oak-core Cargo.toml: wgpu back to 25 (the moved backend code is
  written against that API generation); add the toml/quick-xml/image
  deps oak-common carried.
- lib.rs: drop the duplicate 'pub mod error;'.
- error.rs: unified OAKCORE_* codes; restore Error::new() and
  From<OcioError> from oak-common's error type.
- backend.rs/color.rs: oak_core::/oak_render:: self-references
  rewritten to crate::; the shaderfx-dependent GPU effect test moved
  to oak-render's shaderfx tests (shaderfx depends on oak-node and
  cannot live in oak-core).
- oak-render's error module re-exports oak_core::error::{Error,
  Result}; the OAKRENDER_* codes stay as the public-code contract.
- oak-node jobs.rs: ColorProcessor imported from oak_core::color.
- Integration tests repointed at oak_core::{texture, frame, backend,
  color, colormath}.
- the display-ICC regression test treats an empty OAK_DISPLAY_ICC as
  unset, matching displayicc::env_override_icc.

crates/oak-node/src/sequence.rs

@@ -123,9 +123,9 @@ impl SequenceBehavior {
 
 	/// Apply the default video/audio parameters (C++
 	/// `ViewerOutput::set_default_parameters()`; the config lookups read
-	/// the oakcommon config store directly).
+	/// the oak_core config store directly).
 	pub fn set_default_parameters(&mut self) {
-		let config = oak_common::configstore::ConfigStore::instance();
+		let config = oak_core::configstore::ConfigStore::instance();
 		let width = config.get_int(None, "DefaultSequenceWidth", 1920);
 		let height = config.get_int(None, "DefaultSequenceHeight", 1080);
 		let sample_rate = config.get_int(None, "DefaultSequenceAudioFrequency", 48000);