Add persistent SQLite usage, x402 payment paywall, and MCP server

- SQLite persistence (better-sqlite3): wallet_usage table survives pm2
  restarts, atomic increment via transaction, admin wallet auto-seeded
- x402 paid endpoints (/api/v1/paid/*): agents/bots pay $0.01 USDC per
  scan via Coinbase facilitator, no JWT required
- MCP server (mcp-server.ts): stdio JSON-RPC 2.0 with daybreak_scan_deployer
  and daybreak_scan_wallet tools, auto-pays x402 when private key configured
- Frontend 402 handling: PaymentPrompt component shows when free scans
  exhausted, wallet signs x402 payment, retries via paid endpoint
- Rate limit returns 402 (not 429) with x402 payment details + paid
  endpoint redirect
- Enhanced rug detection (Phase 3.5): mint/freeze authority, deployer
  holdings, top holder %, bundled launch detection with score penalties
- Bug fixes: cache mutation between requests, scans_limit default 10→3,
  MCP dual stdin consumer conflict, payment error visibility in frontend

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Jpatching

.gitignore

@@ -9,6 +9,7 @@ target/
 deployment.json
 *:Zone.Identifier
 data.db
+backend/data/
 *.log
 backend/node_modules/
 backend/dist/

backend/.env.example

@@ -2,3 +2,6 @@ HELIUS_API_KEY=your_helius_key_here
 SOLANA_RPC_URL=https://mainnet.helius-rpc.com/?api-key=YOUR_KEY
 PORT=3001
 JWT_SECRET=your_random_64_char_hex_secret
+TREASURY_WALLET=5rSwWRfqGvnQaiJpW3sb3YKLbxtjVxgc4yrvrHNeNwE2
+X402_PRICE_USD=0.01
+X402_NETWORK=solana