[SECURITY][PAYMENT ROUTING] Reject missing or unknown payment types instead of defaulting to wallet funding

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Summary

Missing or unrecognized Paystack metadata is silently treated as wallet funding. A malformed or legacy provider event can therefore enter the most permissive credit path.

Repository evidence

• app/api/payments/webhook/route.ts:10-15 maps every unknown value to wallet_funding.
• app/api/payments/verify/route.ts:23-28 applies the same fallback.

Scope

• Use an exhaustive parser for supported payment purposes and schema versions.
• Quarantine or ignore events whose purpose is missing, unknown, or inconsistent with the stored payment intent.

Acceptance criteria

• Only explicitly recognized payment purposes reach a financial mutation.
• Rejected events retain a redacted diagnostic record for reconciliation.

Tests

• Cover absent, misspelled, mixed-case, legacy, and malicious payment type values.

Non-goals

• Adding new payment purposes.