Add shape prefix to symbol IDs, fix brand naming, add assets

- Symbol IDs now include shape for uniqueness: {shape}_{brand}_{mode}
  e.g., text-only_paypal_lm, rectangle_visa_la, icon_mastercard_dm
- Fixed brand name inconsistencies:
  - amazon_pay → amazon
  - naverpay → naver_pay
  - p24 → przelewy24
  - direct_debit → bacs (unified BACS Direct Debit name)
- Added font assets (FontAwesome, Material Icons)
- Added MprIconsAssets and MprIconsConfig classes
- Updated preview.html with shape parameter support
- All 752 icons complete (38 payment × 4 shapes × 4 modes + 12 social × 3 shapes × 4 modes)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/material-icons/material-icons.css

@@ -0,0 +1,25 @@
+/* Material Icons - Self-hosted version */
+@font-face {
+  font-family: 'Material Icons';
+  font-style: normal;
+  font-weight: 400;
+  font-display: block;
+  src: url('./fonts/MaterialIcons-Regular.woff2') format('woff2');
+}
+
+.material-icons {
+  font-family: 'Material Icons';
+  font-weight: normal;
+  font-style: normal;
+  font-size: 24px;
+  line-height: 1;
+  letter-spacing: normal;
+  text-transform: none;
+  display: inline-block;
+  white-space: nowrap;
+  word-wrap: normal;
+  direction: ltr;
+  -webkit-font-feature-settings: 'liga';
+  font-feature-settings: 'liga';
+  -webkit-font-smoothing: antialiased;
+}