Python/OpenCV proof of concept plus first native Swift port

Snapshot before the Python POC is removed. The POC (main.py, effects.py,
panel.py, shaders.py, effects/*.glsl, flake.nix) is the reference for the
native app under native/.

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

effects/wave-shift.glsl

@@ -0,0 +1,12 @@
+// RGB split that ripples down the image and gets pushed around by your movement.
+uniform float amount;  // 0.0 .. 0.05 = 0.012
+uniform float waves;   // 1.0 .. 80.0 = 24.0
+uniform float react;   // 0.0 .. 3.0 = 1.0
+
+void main() {
+    vec2 d = vec2(amount * sin(uv.y * waves + time * 3.0), 0.0);
+    d += texture(flow, uv).xy * react;
+    color = vec4(texture(camera, uv + d).r,
+                 texture(camera, uv).g,
+                 texture(camera, uv - d).b, 1.0);
+}