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-task/src/proxy.rs

@@ -353,7 +353,7 @@ impl ProxyTask {
 
 	/// 配置的代理转码并发上限（[1, 16]）。
 	pub fn proxy_max_concurrent() -> i32 {
-		oak_common::configstore::ConfigStore::instance()
+		oak_core::configstore::ConfigStore::instance()
 			.get_int(None, Self::CONFIG_KEY_PROXY_MAX_CONCURRENT, 1)
 			.clamp(1, 16)
 	}
@@ -411,7 +411,7 @@ impl TaskBehavior for ProxyTask {
 		// unification: the old two-stage C ABI getter is gone; an empty
 		// string means "not found"). The `FFmpegPath` config takes
 		// precedence when set (C++ `OAK_CONFIG("FFmpegPath")`).
-		let configured = oak_common::configstore::ConfigStore::instance()
+		let configured = oak_core::configstore::ConfigStore::instance()
 			.get(None, "FFmpegPath")
 			.unwrap_or_default();
 		let ffmpeg_path = ProxyManager::find_ffmpeg(&configured);