fix(gravity): reject offline relayer confirmations

[jamilahmadzai]

Summary

• Reject ConfirmBatch and RelayerSetConfirm submissions when the relayer's stored record is offline.
• Filter stored batch and relayer-set confirmation query results, including both list and specific-confirm endpoints, so offline relayer signatures are not returned as executable bridge material.
• Add regression coverage for both confirmation message paths and for stale stored confirmation query results.
• Keep TRON keeper test relayers active so the shared confirmation tests continue covering the successful active-relayer paths.

Root cause

confirmHandlerCommon loaded the relayer record and verified the external address and signature, but it did not enforce the same Online gate that claim handling already uses. That allowed a slashed/offline relayer to keep submitting valid external signatures for pending bridge work.

Validation

• go test ./x/tron/keeper -run 'TestKeeperTestSuite/(TestQuery_BatchConfirms|Test_msgServer_ConfirmBatch|Test_msgServer_RelayerSetConfirm)' -count=1 -v
• go test ./x/gravity/keeper -run 'TestGravityKeeperTestSuite/TestOfflineRelayer' -count=1 -v
• go test ./x/gravity/keeper -run 'TestGravityKeeperTestSuite/Test(MsgSetRelayerSetConfirm|ClaimWithRelayerOnline|Keeper_DeleteBatchConfirm|LastPendingBatchRequestByAddr|QueryUnbatchedTxs)' -count=1 -v
• go test ./x/tron/keeper ./x/gravity/keeper -count=1
• git diff --check

Fixes #940

Meta Earth bug bounty payout: $MEC via ME Pass address me1ya82w6cjflk9r2qeyfeu64sm7gxtfr7mu62w9j.