fix security issues and bugs found during code review

[YashejShah]

what i found

went through the codebase and found some security + reliability issues worth fixing.

security

• ssrf bypass in url validation — strings.Contains(host, "razorpay.com") can be bypassed with domains like razorpay.com.evil.com. switched to proper suffix matching with isRazorpayURL() that checks exact match or .razorpay.com suffix
• sensitive data in logs — full payment request/response bodies were being logged at INFO level via the MCP hooks. added redactSensitiveFields() that strips out card numbers, tokens, bank account details, cvv etc before anything hits the logs
• credentials in process args — api key/secret were passed as CLI flags in the Dockerfile entrypoint, making them visible via ps aux. removed the --key/--secret flags from ENTRYPOINT since viper already picks up RAZORPAY_KEY_ID/RAZORPAY_KEY_SECRET from env vars
• no startup validation — server would happily start with empty credentials and fail silently on first API call. added early validation in the stdio command that exits with a clear error message
• log file permissions — log files were created with 0666 (world-readable). changed to 0600

bugs & improvements

• expand[] parameter dropping values — ValidateAndAddExpand was overwriting the same map key in a loop, so only the last expand value survived. fixed to accumulate into a slice
• fabricated email addresses — when no email was provided, the code was generating fake emails like 9876543210@mcp.razorpay.com. removed this and made email properly optional
• type assertion safety — added comma-ok pattern to type assertions across payments, orders, and payment_links to prevent panics on unexpected data
• razorpay ID format validation — added validateRazorpayID() helper and applied it to payment_id and order_id extraction to catch malformed IDs early
• unused json import — removed the forced var _ = json.Marshal and its import from integrations/helpers.go
• added .env and coverage.out to .gitignore
• removed committed coverage.out from tracking

tested locally, all existing tests pass.