ui: port game UI framework into library/modules/ui

20 files (~3,830 lines): view protocol, layout, renderer, glyph cache,
fonts, gestures, animation, scroll, stacks, modifiers, etc.

Internal imports rewritten from "ui/..." to "modules/ui/...".
Consumers now `#import "modules/ui"` from any project; no symlink
hacks needed. Verified by compiling game/main.sx without its local
ui/ — resolves via the Phase 6 stdlib fallback.

library/modules/ui/image.sx

@@ -0,0 +1,36 @@
+#import "modules/std.sx";
+#import "modules/ui/types.sx";
+#import "modules/ui/render.sx";
+#import "modules/ui/events.sx";
+#import "modules/ui/view.sx";
+
+ImageView :: struct {
+    texture_id: u32;
+    width: f32;
+    height: f32;
+    tint: Color;
+}
+
+impl View for ImageView {
+    size_that_fits :: (self: *ImageView, proposal: ProposedSize) -> Size {
+        pw := proposal.width ?? self.width;
+        ph := proposal.height ?? self.height;
+        // Maintain aspect ratio: fit within proposal
+        aspect := self.width / self.height;
+        if pw / ph > aspect {
+            Size.{ width = ph * aspect, height = ph };
+        } else {
+            Size.{ width = pw, height = pw / aspect };
+        }
+    }
+
+    layout :: (self: *ImageView, bounds: Frame) {}
+
+    render :: (self: *ImageView, ctx: *RenderContext, frame: Frame) {
+        ctx.add_image(frame, self.texture_id);
+    }
+
+    handle_event :: (self: *ImageView, event: *Event, frame: Frame) -> bool {
+        false;
+    }
+}