Every improvement, in order.

Bid calculator fix

• FixThe bid modal's price calculator no longer sticks on “Calculating…”. The calculation now re-runs every time the modal opens (it previously ran only on page load, so the pay button never resolved on first open).

Security hardening pass

• SecurityRace-safe webhook idempotency: concurrent duplicate deliveries now resolve to “already recorded” via the unique payment constraint instead of erroring into provider retry storms. Applied to all four webhook routes (Stripe, Dodo, Razorpay, generic).
• SecurityError messages no longer leak internals: webhook and checkout failures return generic messages while details go to server logs.
• SecurityProvider configuration is no longer public: GET /api/checkout no longer exposes per-provider setup flags.
• SecurityDestructive seed route is fail-closed: /api/dev/seed now requires ENABLE_DEV_SEED=true even outside production, so a staging deploy can never be wiped by an unauthenticated request.
• SecuritySpoof-resistant rate limiting: client IP prefers x-real-ip over the spoofable end of X-Forwarded-For, and buckets are pruned and capped against memory-exhaustion attacks.
• SecurityDNS-level SSRF protection: scraped hostnames are DNS-resolved and re-checked against the private-IP blocklist before fetching and after redirects.
• FeatureDocumented security model in the README: webhook verification, sandbox gates, SSRF design, and rate limits.

Initial release

• FeaturePay-to-rank bidding engine with atomic, race-safe transactions and cumulative-total ranking.
• FeatureThree leaderboards from one payment: All-Time, rolling 24H, and Daily UTC archives.
• FeatureLive activity ticker, KPI stats bar, category filters, and confetti on paid bids.
• FeatureSSRF-hardened OpenGraph scraper: paste any URL or @handle for instant listing autofill.
• FeatureStripe, Dodo, and Razorpay webhooks with signature verification, plus a zero-key sandbox mode.
• FeatureSQLite by default with a one-line switch to Postgres; seed script included.
• FeatureOne-file rebrand (name, currency, rules, categories, FAQ) in the warm paper theme with the BidKit mark.