feat: add Gravity (L1, chainId 127001) to popular networks

[AshinGau]

Description

Adds Gravity (Gravity's L1 mainnet, chainId 127001 / 0x1f019) to the popular networks list (FEATURED_RPCS), wired exactly like the existing custom-RPC popular networks (Tempo, Arc). The brand icon ./images/gravity.svg already exists in the repo and is reused, so no new asset is added.

This is a different chain from the existing Gravity Alpha Mainnet (0x659 / 1625, Gravity's L2): different layer, different chainId. The new constant is GRAVITY (vs. the existing GRAVITY_ALPHA_MAINNET), so there is no name/identifier collision.

Network details (consistent with the merged chainid.network registration):

Field	Value
Name	Gravity
Chain ID	127001 (0x1f019)
Native currency	G (18 decimals)
RPC	https://mainnet-rpc.gravity.xyz
Block explorer	https://mainnet-explorer.gravity.xyz (EIP-3091)

• ethereum-lists/chains: Add Gravity Chain (ID: 127001) ethereum-lists/chains#8380 (merged)
• chainlist: https://chainlist.org/chain/127001

Manual testing steps

1. Network selector → Add a network
2. "Gravity" appears in the popular networks list with its icon
3. Add it and confirm the RPC and block explorer resolve

[github-actions]

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[AshinGau]

I have read the CLA Document and I hereby sign the CLA