refactor: remove BlockRun provider, retain Claw402 as sole x402 payment provider

Remove all BlockRun (Base + Solana wallet) references from codebase:
- Delete blockrun_base.go, blockrun_sol.go, wallet setup docs, icon
- Move shared EIP-712 signing code to x402.go for Claw402 reuse
- Clean up provider constants, model lists, UI components, translations
- Update all README files (EN + 6 i18n) and getting-started docs

web/public/icons/blockrun.svg

@@ -1,6 +0,0 @@
-<svg viewBox="0 0 100 100" fill="none" xmlns="http://www.w3.org/2000/svg">
-  <rect x="30" y="20" width="55" height="60" rx="14" stroke="#FFFFFF" stroke-width="8" fill="none"/>
-  <path d="M15 35 L25 35" stroke="#FFFFFF" stroke-width="6" stroke-linecap="round"/>
-  <path d="M10 50 L25 50" stroke="#FFFFFF" stroke-width="6" stroke-linecap="round"/>
-  <path d="M15 65 L25 65" stroke="#FFFFFF" stroke-width="6" stroke-linecap="round"/>
-</svg>