Ask the platform what colour the screen actually is

FR-DSP-8's acquisition half. `dr_plat::display` surveys the session's
displays and reduces each one's profile to an output space the pipeline
can encode into, stating the mechanism per display server as
FR-PLAT-LIN-2 requires:

  - X11 reads the `_ICC_PROFILE` / `_ICC_PROFILE_<n>` root-window
    properties, enumerating and numbering the outputs through RandR,
    which also yields the rectangles a window move is measured against.
  - Wayland binds `wp_color_manager_v1` and asks each `wl_output` for
    its image description, accepting either an ICC profile on a file
    descriptor or primaries stated as chromaticities.
  - Where neither answers, sRGB is assumed and the reason travels with
    it as data rather than into a log, so the About page can say which
    path the session is on.

A display profile is a measurement of one panel and is none of the four
spaces the pipeline knows. Rather than grow an ICC engine, the profile
is reduced to D50-adapted colorants and matched against the four; a
match that is merely nearest is marked as such and shown as such.

Verified on this machine: mutter 50 advertises the colour-management
global and reports eDP-1 as sRGB, and the same session forced onto X11
enumerates the output through RandR and correctly finds no atom.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Cargo.toml

@@ -115,6 +115,25 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 base64 = "0.23"
 
+# Display-server clients, for FR-DSP-8's per-display profile acquisition.
+#
+# Neither is a new cost: winit already builds both, so the versions are the
+# ones Slint's backend has resolved to and pinning anything else here would
+# compile a second copy. Both are pure Rust — x11rb speaks the X11 wire
+# protocol itself rather than binding libxcb, and wayland-client binds
+# libwayland only under a feature that is off — which keeps the Android
+# cross-compile a plain Rust dependency graph, the same criterion as the TLS
+# and SQLite choices above. They are declared under a target predicate that
+# excludes Android, where neither display server exists.
+#
+# `staging` on wayland-protocols is what carries `wp_color_manager_v1`: the
+# colour-management extension is still staging upstream, which is the
+# protocol-level statement of the thing FR-DSP-8 anticipates when it says
+# Wayland's colour management "is not universally available".
+x11rb = { version = "0.13", features = ["randr"] }
+wayland-client = "0.31"
+wayland-protocols = { version = "0.32", features = ["client", "staging"] }
+
 # Platform secure storage: Secret Service on Linux, Keystore on Android
 # (FR-NC-2). Credentials never touch the catalog or a plain file.
 # keyring 4 restructured its features: `v1` is the default set and brings