superseed-sepolia: add Karst hardfork time (1781712001 = 2026-06-17 16:00:01 UTC)

OP Sepolia network-wide Karst activation. op-node v1.19.0 (pinned) and
conduit-op-reth:latest are Karst-aware; op-node v1.17.0 introduced Karst.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

op/superseed/sepolia/genesis.json

@@ -25,6 +25,7 @@
       "holoceneTime": 1732633200,
       "isthmusTime": 1744905600,
       "jovianTime": 1768978801,
+      "karstTime": 1781712001,
       "terminalTotalDifficulty": 0,
       "terminalTotalDifficultyPassed": true,
       "optimism": {

op/superseed/sepolia/rollup.json

@@ -36,6 +36,7 @@
   "holocene_time": 1732633200,
   "isthmus_time": 1744905600,
   "jovian_time": 1768978801,
+  "karst_time": 1781712001,
   "pectra_blob_schedule_time": 1742486400,
   "batch_inbox_address": "0x3a81f59e6bf4238d1ed202f3b06389454de3f204",
   "deposit_contract_address": "0x7a0db8c51432d2c3eb4e8f360a2eeb26ff2809fb",