World: add skybox changer

New Visuals -> Skybox card with a runtime sv_skyname override using the same
mechanism as the stock skybox_swapper entity. The choice list is the HL2
skybox set extracted from the game VPKs.

The map's own sky is captured from loaded materials (SkyBox group, parsing
skybox/<name>... face names) before the first override, so turning the
feature off or picking "Map default" restores it; a level change restores it
implicitly. Sky changes invalidate the world tint so new sky materials are
tinted as well.

GUI: add a CK_CHOICE control (value box with < / > zones).

1 files changed, 15 insertions, 0 deletions

diff --git a/CONTEXT.md b/CONTEXT.md
index 741050d..f2b091a 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -358,6 +358,21 @@ vocabulary / decisions.
 - End is clamped above Start. Re-applied on level change via
   `fog_invalidate()`. Saved as `[fog] active/bind/r/g/b/start/end/skybox/disable`.
 
+### Skybox changer
+
+- `sv_skyname <name>` through `ClientCmd`, the same mechanism the stock
+  `skybox_swapper` entity uses. Choice list is the HL2 skybox set from the
+  game's VPK (no episode-only skies, so a selected sky always exists).
+- Before the first override of a map, the map's own sky is captured by
+  scanning loaded materials in the `SkyBox textures` group and parsing
+  `skybox/<name>(_hdr|_ldr)?(rt|bk|lf|ft|up|dn)`. Disabling the feature (or
+  choosing "Map default") restores that name; a level change also restores it
+  naturally, so `skybox_invalidate()` just drops the captured state.
+- Changing the sky invalidates the world tint so the freshly loaded sky
+  materials get the sky colour.
+- Saved as `[skybox] active/bind/choice`. The GUI uses a `CK_CHOICE`
+  control (value box with `<`/`>` hit zones).
+
 ## Logging
 
 - `/tmp/hl2hake.log` is opened once at startup with `"w"` (so it only contains