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-codec/src/encodingparams.rs

@@ -269,10 +269,10 @@ impl EncodingParams {
 		}
 	}
 
-	/// Load from a compact XML preset string (oakcommon C++ XmlStreamReader).
+	/// Load from a compact XML preset string (oak_core C++ XmlStreamReader).
 	///
 	/// # CPP-PARITY
-	/// `EncodingParams::load` — uses oakcommon's C++ `XmlStreamReader`
+	/// `EncodingParams::load` — uses oak_core's C++ `XmlStreamReader`
 	/// (`src/common/src/xmlutils.h`), a C++-to-C++ coupling the bridge
 	/// cannot cover (NOTES.md §7). Preserves the load_v1 bug of not
 	/// assigning `custom_range`.
@@ -524,7 +524,7 @@ impl EncodingParams {
 // ---------------------------------------------------------------------------
 // Minimal XML helpers for the round-trip `load`/`save_to_string`.
 //
-// CPP-PARITY: the C++ `load`/`save_to_string` go through oakcommon's
+// CPP-PARITY: the C++ `load`/`save_to_string` go through oak_core's
 // `XmlStreamReader`/`XmlStreamWriter` (a C++-to-C++ coupling the Rust bridge
 // cannot cover, NOTES.md §7). Rather than returning `Err`, this port keeps a
 // minimal but faithful round-trip for the fields representable without the