feat: implement ledger-bounded policy renewal with premium recalc, cl…

[GoodnessJohn]

Implements the full policy renewal flow, enforcing strict ledger-bounded windows, deterministic premium recalculation, open-claim blocking, checked arithmetic, and structured event emission.

Changes

New files

• renewal.constants.ts — window constants with full inline docs on inclusive/exclusive semantics and server-client skew guidance
• dto/renewal.dto.ts — request/response DTOs and PolicyRenewedEvent interface
• renewal.service.ts — core orchestration: window validation, premium recalc, open-claim enforcement, i128 overflow guard, event emission
• renewal.controller.ts — POST /policy/renewal/quote and POST /policy/renewal/build-transaction
• renewal.service.spec.ts — 30 unit tests covering all boundary conditions and edge cases

Modified files

• soroban.service.ts — adds buildRenewPolicyTransaction() and BuildRenewalTransactionResult type
• policy.module.ts — wires RenewalController and RenewalService

Renewal window semantics

Half-open interval [windowOpen, windowClose):

• windowOpen = endLedger - RENEWAL_OPEN_LEDGERS_BEFORE_EXPIRY (inclusive, ~7 days before expiry)
• windowClose = endLedger + RENEWAL_GRACE_LEDGERS_AFTER_EXPIRY (exclusive, ~1 day grace after expiry)

Violations return RENEWAL_TOO_EARLY or RENEWAL_TOO_LATE with ledger numbers in the message.

Open-claim rule

Renewal is blocked when any claim has status PENDING (on-chain: Processing). APPROVED, PAID, and REJECTED claims do not block. Returns OPEN_CLAIM_BLOCKS_RENEWAL.

Event emission

PolicyRenewed is emitted on renewalBus exactly once per successful buildRenewalTransaction call — never on quote-only calls or failed validations.

Closes #9

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