feat(ugc): icon light matched to the game, debounce, shared car icons, purge, icon editor

Brighter icons: a world light, a fill from the camera, a highlight, exposure
and contrast; with the defaults the icons' mean luminance matches the game's
own model icons (118 against 120 on a scratch set). Every icon parameter is
listed once (UgcIconParams: key, setting, range, default); the settings,
the dashboard's settings entries and the icon editor come from that list.
Presets per kind (player models, each car or rocket build type from
ModularBuildComponent) and overrides per model or module combination are in
ugc_icon_settings.

Saved models wait ugc_debounce_seconds (sharedconfig) after the owner's last
save before they're made (ugc.process_after); a client asking for one, the
owner leaving the world or a reset ends the wait.

Cars and rockets: one icon per combination of modules (sorted LOTs), shared
by every build of it; builds of a combination made already are marked made
right away, the client's per-blueprint downloads serve the shared files.

The dashboard can delete one item's files, purge by filter or all, preview
icons with any values on the UGC server (/admin routes, master password),
save presets and overrides, and draw a kind's icons again (icons only).

Migrations dlu/mysql/86 and dlu/sqlite/69. Not done yet: the dashboard
editor's lighting controls in the page script (routes are there), docs for
it, the empty-model state, /ugc?item= links, the shared fetch helper; the
storage size and property loading bugs are next.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dUgcServer/UgcRender.h

@@ -28,9 +28,8 @@ namespace UgcRender {
 	};
 
 	/**
-	 * The icon, set up like LU Toolbox's icon renderer (the BrickBuild scene of its UGC render add-on): a 50 mm lens
-	 * (39.6 degree field of view) looking from 53.4 degrees around and 19.5 above, framed at 1.03, a sun of strength
-	 * 2.5 from 21 around and 50.3 above with soft shadows, and a grey (0.192) world light, darkened by ambient occlusion.
+	 * How an icon is drawn. The values that can be set (settings icon_*, presets and overrides) are listed once, with
+	 * their ranges and shipped defaults, in UgcIconParams; the ones here are only what the struct starts with.
 	 */
 	struct IconOptions {
 		int size{ 128 };
@@ -39,13 +38,20 @@ namespace UgcRender {
 		float pitchDegrees{ 19.54f }; // camera above the model
 		float fovDegrees{ 39.6f };
 		float margin{ 1.03f };       // 1 fills the icon, more leaves a border
+		float offsetX{};             // the model moved right by this share of the icon's width (after framing)
+		float offsetY{};             // and up by this share of its height
 		glm::mat4 modelRotation{ 1.0f }; // applied to the model before the camera looks at it
 		float sunYawDegrees{ 21.0f };
 		float sunPitchDegrees{ 50.3f };
 		float sunStrength{ 2.5f };
-		float ambient{ 0.192f };
-		bool shadows{ true };
-		AoOptions ao{ true, 5.0f, 32, 1.0f, 0.0f };
+		float ambient{ 0.192f };     // the world light (radiance) every face gets
+		float fill{ 0.0f };          // a light from the camera (irradiance), what lifts the sides facing the viewer
+		float specular{ 0.0f };      // the sun's highlight on the plastic
+		float shininess{ 60.0f };    // how tight the highlight is
+		float exposure{ 1.0f };      // everything times this before it's written as sRGB
+		float contrast{ 1.0f };      // around the middle grey of the sRGB result
+		float shadows{ 1.0f };       // how much the sun's shadows darken, 0 to 1
+		AoOptions ao{ false, 5.0f, 32, 1.0f, 0.0f };
 	};
 
 	// The model drawn from the icon's camera, framed to fit, on a transparent background. `opaqueAo`: the opaque mesh's