feat(sc-001): implement on-chain claim registry

[Charity5654]

Add the foundational ClaimRegistry contract for TruthBounty V2. Every claim must originate from this registry, making it the canonical on-chain source of truth for all protocol state.

Changes:

• contracts/interfaces/IClaimRegistry.sol — clean interface for all downstream modules (Verification Engine, Settlement Engine, etc.) Defines ClaimStatus enum, Claim struct, events, custom errors, and all required view/write function signatures.

• contracts/ClaimRegistry.sol — full implementation:

  • permissionless createClaim() with strict input validation
  • sequential, monotonic, never-reused claim IDs starting at 1
  • immutable claim metadata (creator, statement, evidenceCID, createdAt)
  • updateClaimStatus() gated by REGISTRY_UPDATER_ROLE
  • view functions: getClaim, claimExists, totalClaims, getClaimCreator, getClaimStatus
  • ClaimCreated and ClaimStatusUpdated events for off-chain indexing
  • custom errors: InvalidStatement, InvalidCID, InvalidDeadline, ClaimNotFound, UnauthorisedStatusTransition, InvalidStatusTransition
  • packed struct layout for gas efficiency
  • AccessControl (OZ v5) for role management

• test/ClaimRegistry.test.ts — 54 tests:

  • deployment, success cases, statement/CID/deadline validation, registry behaviour, getClaim, getClaimCreator, getClaimStatus, updateClaimStatus, immutability, access control, gas benchmarks

• docs/gas-benchmarks-claim-registry.md — gas benchmark documentation createClaim: 255,308 gas | getClaim: 45,155 gas

• .gas-snapshots.json — updated with ClaimRegistry baseline figures

Pre-existing compilation fixes (unblocked our tests):

• contracts/TruthBounty.sol: add missing ERC20 import
• contracts/bootstrap/BootstrapController.sol: add PAUSER_ROLE, GOVERNANCE_ROLE() to ITruthBountyWeighted interface, remove erroneous 'view' modifier from _validateConfiguration
• contracts/deployment/MigrationManager.sol: add PAUSER_ROLE
• hardhat.config.ts: add viaIR:true to fix RewardEngine stack-too-deep

Test results: 54/54 ClaimRegistry tests pass
365 total passing | 28 pre-existing failures (unrelated modules)

Closes #281