Redesign Purple theme with proper contrast and professional chart axes

Rebuilt the purple color palette from scratch using a 4-level luminance
scale (~3-5x jump per level: #06000f → #110028 → #1d0845 → #3a158a),
matching the approach of high-contrast Bootswatch dark themes (Darkly,
Cyborg). All contrast ratios are now WCAG-compliant: body text 16:1,
card header white text 8.5:1, primary button 5.5:1.

Chart axis improvements: Y-axis large numbers abbreviated (1.4M, 568K),
X-axis max 6 ticks at 30° rotation, Inter font throughout, dark-glass
tooltips, network_charts settings added to settings.json.tmpl with
transparent canvas background

docker/settings.json.tmpl

@@ -98,6 +98,40 @@
         "enabled": true,
         "display_order": 4
       },
+      "network_charts": {
+        "nethash_chart": {
+          "enabled": true,
+          "chart_title": { "enabled": false, "title_text": "", "alignment": "center", "color": "#666", "font": { "family": "Arial", "size": 14, "weight": "bold" } },
+          "legend": { "enabled": true, "position": "bottom" },
+          "bgcolor": "transparent",
+          "line_color": "rgba(54,162,235,1)",
+          "fill_color": "rgba(54,162,235,0.2)",
+          "crosshair_color": "#aaa",
+          "block_line": { "enabled": true, "block_line_color": "rgba(0,128,0,0.2)" },
+          "round_decimals": 3,
+          "chart_height": 320,
+          "full_row": false,
+          "stretch_to_fit": false
+        },
+        "difficulty_chart": {
+          "enabled": true,
+          "chart_title": { "enabled": false, "title_text": "", "alignment": "center", "color": "#666", "font": { "family": "Arial", "size": 14, "weight": "bold" } },
+          "legend": { "enabled": true, "position": "bottom" },
+          "bgcolor": "transparent",
+          "pow_line_color": "rgba(255,99,132,1)",
+          "pow_fill_color": "rgba(255,99,132,0.2)",
+          "pos_line_color": "rgba(255,161,0,1)",
+          "pos_fill_color": "rgba(255,161,0,0.2)",
+          "crosshair_color": "#aaa",
+          "block_line": { "enabled": true, "block_line_color": "rgba(0,128,0,0.2)" },
+          "round_decimals": 3,
+          "chart_height": 320,
+          "full_row": false,
+          "stretch_to_fit": false
+        },
+        "reload_chart_seconds": 60,
+        "sync_charts": true
+      },
       "custom_menus": []
     },
     "page_footer": {