Fix source file naming, rebuild sprites, add dev tools

- Fix bank_transfer -> bank naming in icon/square shapes
- Fix quote_la -> quote_lm in light-mode directories
- Fix rectangle naming (amazon_pay, bacs, naverpay, p24)
- Fix case sensitivity (LinkedIn -> linkedin, Bancontact -> bancontact, etc.)
- Add _lm suffix to rectangle/light-mode files
- Copy X icon to full-logo and text-only (same symbol)
- Add preview.html for visual testing
- Add .htaccess restricting access to dev IP
- Update README with correct lowercase brand names

All 38 payment brands and 12 social brands now complete.

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

README.md

@@ -193,7 +193,7 @@ copy(
 
 **Available payment brands (38):**
 
-afterpay, alipay, alma, amazon_pay, american_express, apple_pay, bacs, bancontact, bank, Billie, blik, cartes_bancaires, cod, credit_pay, eps, google_pay, ideal, jcb, kakao_pay, klarna, link, mastercard, mobilepay, multibanco, naverpay, p24, payco, paypal, pickup, point_of_sale, revolut, samsung_pay, satispay, sepa, twint, unionpay, visa, wechat_pay
+afterpay, alipay, alma, amazon_pay, american_express, apple_pay, bacs, bancontact, bank, billie, blik, cartes_bancaires, cod, credit_pay, eps, google_pay, ideal, jcb, kakao_pay, klarna, link, mastercard, mobilepay, multibanco, naverpay, p24, payco, paypal, pickup, point_of_sale, quote, revolut, samsung_pay, satispay, sepa, twint, visa, wechat_pay
 
 ### Social Icons
 
@@ -207,7 +207,7 @@ afterpay, alipay, alma, amazon_pay, american_express, apple_pay, bacs, bancontac
 
 **Available social brands (12):**
 
-amazon, apple, facebook, google, LinkedIn, microsoft, outlook, paypal, reddit, tiktok, x, yahoo
+amazon, apple, facebook, google, linkedin, microsoft, outlook, paypal, reddit, tiktok, x, yahoo
 
 ### Icon ID Format