color: non-sRGB preview, per-monitor display ICC, pipeline hardening

Preview now follows the project output colorspace end to end: the
display chain derives its content space from the project's OutputColorSpec
instead of a hardcoded sRGB name, self-managed ICC transforms go through
an XYZ D65 interchange stage (OCIO cie_xyz_d65_interchange) for non-sRGB
targets, and the platform layer declares the content colorspace (gpui
submodule bump). macOS defaults to OS-managed (fixes wide-gamut UI
oversaturation); Windows ACM warns once on non-sRGB targets.

Multi-monitor: the display ICC is looked up per the window's current
screen (macOS display id, Windows per-monitor DC, X11 RandR output
profile) with a throttled poll that invalidates frame caches on moves.

Pipeline precision: 10-bit+ sources fall back to YUV444P16LE + a Rust
matrix conversion when swscale lacks F32 output (no more 8-bit
truncation); BT.709/2020 SDR decodes with BT.1886 gamma 2.4 instead of
the sRGB EOTF; working-space compositing no longer clamps RGB to [0,1]
(alpha still clamped); the output node clamps to the target gamut;
frames without colorimetry metadata convert with BT.709 defaults
(warned once) instead of passing through; scopes read the
output-colorspace signal on both F32 paths.

Also: only emit rerun-if-changed for .env when it exists (a missing file
made every build fully dirty).

crates/oak-codec/src/decoder.rs

@@ -145,6 +145,21 @@ pub struct RetrieveVideoParams {
 	pub target_size: Option<(u32, u32)>,
 }
 
+/// The colorimetry of a decoded frame, as carried out of the bitstream
+/// (raw ISO/IEC 23001-8 / H.273 code points — the same numbering FFmpeg's
+/// `AVCodecParameters` uses). The render layer maps these to its input
+/// transform (source colorspace → the pipeline working space).
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
+pub struct DecodedColorMeta {
+	/// Color primaries code point (`AVCOL_PRI_*`; 0/2 = unknown).
+	pub color_primaries: i32,
+	/// Transfer characteristic code point (`AVCOL_TRC_*`; 0/2 = unknown).
+	pub color_trc: i32,
+	/// True when the decoded RGB is full range (the YUV→RGB used the
+	/// full-range coefficients).
+	pub full_range: bool,
+}
+
 /// `Decoder::RetrieveAudioStatus` — outcome of an audio retrieve.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum RetrieveAudioStatus {