feat: implement evolution and gradient systems with settings modal

- Add EvolutionController to manage spawning and physics of icons.
- Introduce GradientController for animated gradient backgrounds.
- Create iconLoader for fetching and caching SVG icons.
- Implement modal functionality for settings adjustments.
- Connect UI controls to controllers via SettingsController.
- Add CSS styles for gradient animations, icons, and modal.
- Create utility functions for color manipulation in gradients.

src/js/main.js

@@ -0,0 +1,37 @@
+/**
+ * main.js
+ * Application entry point.
+ *
+ * Responsibilities:
+ *  - Instantiate all controllers
+ *  - Wire the settings button to the modal
+ *  - Kick off the gradient and evolution system
+ *
+ * Keep this file thin — business logic lives in the controllers.
+ */
+
+import { GradientController }  from './gradient.js';
+import { ModalController }     from './modal.js';
+import { SettingsController }  from './settings.js';
+import { EvolutionController } from './evolution.js';
+import { DEFAULTS }            from './constants.js';
+
+// ── Initialise controllers ─────────────────────────────────
+const gradient  = new GradientController();
+const modal     = new ModalController();
+const evolution = new EvolutionController();
+
+// SettingsController bridges UI → gradient + evolution
+// eslint-disable-next-line no-unused-vars
+const settings  = new SettingsController(gradient, evolution);
+
+// ── Wire up settings button ────────────────────────────────
+document.getElementById('settingsBtn').addEventListener('click', (e) => {
+  modal.open(/** @type {HTMLElement} */ (e.currentTarget));
+});
+
+// ── Boot gradient ──────────────────────────────────────────
+gradient.init(DEFAULTS.GRADIENT_COLOR);
+
+// ── Boot evolution (async — loads icons.json + warms SVG cache) ──
+evolution.init(document.getElementById('evolutionContainer'));