feat: add anomaly threshold checks for scoring (#45)

[Escelit]

Closes #45

What this does

Adds a lightweight anomaly signal to the scoring pipeline. When a score
or retention ratio falls outside the expected normal range, the system
logs a server-side warning, blocks minting, and shows an alert banner
in the UI.

Normal behavior

• Score range: 0–~1000 for real testnet wallets (Platino is the ceiling).
• Retention ratio: 0–1 (on-chain balance ≤ total ever deposited).
• No anomaly field in the response → no banner, minting proceeds normally.

Thresholds (api/calculate-score.js)

Constant	Value	Rationale
SCORE_ANOMALY_THRESHOLD	2000	2× above Platino; unreachable under normal use
RETENTION_ANOMALY_THRESHOLD	5	Balance > 5× deposited is implausible

Changes

• api/calculate-score.js — checks both thresholds, emits console.warn,
  adds anomaly: true to the response JSON.
• api/evaluate-and-mint.js — reads the flag; returns HTTP 422
  (status: "anomaly") and blocks minting when set.
• src/context/AppContext.tsx — exposes scoreAnomaly / setScoreAnomaly
  globally.
• src/components/CreditSection.tsx — reads data.anomaly from the
  polling response and renders an amber AlertCircle banner.

How to simulate the trigger

curl -X POST http://localhost:3000/api/calculate-score \
  -H 'Content-Type: application/json' \
  -d '{"address": "<any_testnet_wallet_with_balance>", "totalDeposited": 1}'

If the wallet's on-chain balance exceeds 5 XLM, retention > 5 and the
anomaly fires. Look for [ANOMALY] in the server log and "anomaly": true
in the JSON response.

Signal to watch after deploy

Monitor server logs for [ANOMALY]. A spike for a single wallet or across
many wallets in a short window is the operational signal to investigate.

Threshold review note

Both constants are at the top of api/calculate-score.js with inline
comments. Re-evaluate them in a future PR once a baseline of real score
distributions is available from production traffic.

[vercel]

@Escelit is attempting to deploy a commit to the alankcr1-6443's projects Team on Vercel.

A member of the Team first needs to authorize it.

[drips-wave]

@Escelit Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits