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).

Cargo.lock

@@ -4729,6 +4729,7 @@ dependencies = [
  "gpui_widgets",
  "half",
  "image",
+ "log",
  "oak-audio",
  "oak-codec",
  "oak-common",
@@ -4910,6 +4911,7 @@ version = "0.5.0"
 dependencies = [
  "libc",
  "oak-codec",
+ "oak-common",
  "oak-core",
  "oak-node",
  "oak-plugin",