feat: add BlockRun wallet provider for pay-per-request AI access (#1408)

Integrates BlockRun (blockrun.ai) as a new AI provider option via x402
micropayment protocol, allowing users to access top AI models with USDC
without requiring individual API keys.

- Add BlockRun Base (EVM) and Solana wallet providers to model selector
- Implement x402 v2 EIP-712 payment signing for Base (mcp/blockrun_base.go)
- Implement x402 v2 SPL TransferChecked signing for Solana (mcp/blockrun_sol.go)
- Wire blockrun-base and blockrun-sol into trader factory (auto_trader.go)
- Register both providers in supported models API (server.go)
- Add BlockRun card UI with wallet key input in Step 0/1 of model config modal
- Add BlockRun SVG icon and ModelIcons support
- Add setup guides for Base and Solana wallet configuration (docs/)
- Available flagship models: GPT-5.4, Claude Opus 4.6, Gemini 3.1 Pro,
  Grok 3, DeepSeek Chat, MiniMax M2.5

docs/getting-started/README.md

@@ -44,6 +44,19 @@ Use custom AI models or third-party OpenAI-compatible APIs:
 
 ---
 
+### 💳 BlockRun Wallet (Pay-per-Request, No API Key)
+
+Access all top AI models by paying with USDC — no API key signup required.
+
+| Provider | Guide | Payment Network |
+|----------|-------|-----------------|
+| BlockRun (Base Wallet) | [blockrun-base-wallet.md](blockrun-base-wallet.md) | Base (EVM) · USDC |
+| BlockRun (Solana Wallet) | [blockrun-sol-wallet.md](blockrun-sol-wallet.md) | Solana · USDC |
+
+**How it works:** Each AI request automatically pays a micro-USDC fee via the [x402 payment protocol](https://blockrun.ai). Your private key signs the payment authorization — no funds leave your wallet until the AI response is delivered.
+
+---
+
 ## 🔑 Prerequisites
 
 Before starting, ensure you have: