Keep testnet Seal defaults on legacy key servers

[harrymove-ctrl]

Title

Keep default Seal testnet config on legacy Mysten independent key servers

Summary

This keeps the relayer/sidecar default Seal testnet configuration on the original Mysten independent key server pair instead of switching the default to Mysten’s committee aggregator.

The committee aggregator is still documented and supported through SEAL_SERVER_CONFIGS, but it is no longer the built-in default. This avoids breaking decryptability for existing memories encrypted with the previous testnet key server objects.

Changes

• Restored testnet default Seal config to the two original Mysten independent key servers:
  • 0x73d05d62c18d9374e3ea529e8e0ed6161da1a141a94d3f76ae3fe4e99356db75
  • 0xf5d14a81a982144ae441cd7d64b09027f116a468bd36e7eca494f750591623c8
• Added an inline comment explaining why the default stays on the old key servers.
• Kept Mysten’s committee aggregator available as an opt-in SEAL_SERVER_CONFIGS override:
  • 0xb012378c9f3799fb5b1a7083da74a4069e3c3f1c93de0b27212a5799ce1e1e98
  • https://seal-aggregator-testnet.mystenlabs.com
• Updated docs/env examples to explain:
  • default independent key server behavior
  • committee aggregator opt-in path
  • why existing deployments should not switch until old data is migrated or re-encrypted
• Updated Seal config tests for the reverted default behavior.

Test Plan

• npm test --prefix services/server/scripts
• git diff --check

Notes

This intentionally does not make the committee aggregator the default yet because changing the key server object used for new encryption can make older encrypted memories fail to decrypt unless deployments explicitly keep the old key servers or migrate/re-encrypt data first.

Addresses MEM-49.