feat: add interactive timeline visualization for class times

Implements a canvas-based timeline view with D3 scales showing class
counts across subjects. Features drag-to-pan, mouse wheel zoom, subject
filtering, hover tooltips, and smooth animations. Timeline auto-follows
current time and supports keyboard navigation.

web/package.json

@@ -20,6 +20,9 @@
     "@sveltejs/vite-plugin-svelte": "^5.0.3",
     "@tailwindcss/vite": "^4.0.0",
     "@tanstack/table-core": "^8.21.3",
+    "@types/d3-scale": "^4.0.9",
+    "@types/d3-shape": "^3.1.8",
+    "@types/d3-time-format": "^4.0.3",
     "@types/node": "^25.1.0",
     "bits-ui": "^1.3.7",
     "clsx": "^2.1.1",
@@ -33,6 +36,9 @@
     "vitest": "^3.0.5"
   },
   "dependencies": {
+    "d3-scale": "^4.0.2",
+    "d3-shape": "^3.2.0",
+    "d3-time-format": "^4.1.0",
     "date-fns": "^4.1.0",
     "overlayscrollbars": "^2.14.0",
     "overlayscrollbars-svelte": "^0.5.5"