v6 — Enable globalfee minimum (0.01udgn) + admin & btc-relayer fee exemption + 1500ms block time

Summary

Upgrade dungeon-1 to v6. What changes at the upgrade height: 1. x/globalfee minimum gas price set to 0.01udgn (currently 0 — txs are effectively free, which has been exploited by retry-loop bots and adds noise to validators). Non-exempt txs must attach >= 0.01udgn/gas. 2. Fee-exempt addresses (zero-fee txs allowed) — wired in the v6 binary's ante chain: - Admin / treasury: dungeon13x4pynlp86prhcmtns742kgsgu7pjtzj72eycc - BTC relayer: dungeon1dflpa6dnpkn5ft4tyzkpwdhvz6l7wng06qn665 3. Block time tuned to 1500ms (faster UX for casino + DEX swaps). 4. Dead IBC channel JSON config files removed (cosmetic). Validators MUST swap to the v6 binary at height 14897749 or be halted. Target height assumes ~3 day voting period + ~1 day buffer for binary distribution at current ~1.08s/block. Binary release: github.com/Crypto-Dungeon/dungeonchain/releases (will be tagged v6.0.0 once this proposal passes). Build from main HEAD or use the published binary. This upgrade does NOT change SDK or wasmd versions — those are deferred to a future v7 ceremony alongside Alliance module + bulk-memory wasm capability.