v4: normalize Paytm and Kotak notifications

[Phloraxx]

Scope

Fifth stacked PayGate v4 implementation slice. Depends on PR #46.

Implements

• pure server-side notification normalization; no HTTP/Android wiring yet
• Paytm Business notification parser for com.paytm.business
• Kotak credit parser for Google Messages notifications
• Google Messages package alone is insufficient: Kotak marker + genuine incoming-credit wording are required
• extracts exact amount, payer name and payer UPI ID when available
• Paytm uses explicit Received on ... time when present, otherwise Android notification post time
• Kotak currently uses notification post time unless a trustworthy message timestamp parser is added later
• .00 amounts are rejected as non-PayGate
• refunds, reversals, cashback, settlement, debit/purchase wording and unrelated messages are rejected
• no UTR/RRN requirement or extraction in the v4 contract
• GPay remains unsupported in v4.0

Tests

Covers the captured Paytm notification format, Paytm fallback time, .00, refund/debit/settlement rejection, Kotak sender/profile inference, UPI extraction without reference IDs, rejection of other-bank Google Messages, OTP/debit/cashback rejection, and unsupported GPay. Unit/race/vet pass locally.

Safety

Pure parsing module only. No production listener, route, match or state mutation is wired yet.