[Mainnet] Update frontend + SDK constants for Base mainnet

[realproject7]

Context

After StoryFactory is deployed to Base mainnet (plotlink-contracts#21), update all frontend and SDK constants to point at mainnet.

Scope

lib/contracts/constants.ts

• Set STORY_FACTORY mainnet address (from deploy output)
• Set PLOT_TOKEN mainnet = 0xF8A2C39111FCEB9C950aAf28A9E34EBaD99b85C1 (PL_TEST)
• Update RESERVE_LABEL mainnet from "$PLOT" to "PL_TEST" (test phase)

packages/sdk/src/constants.ts

• Add STORY_FACTORY_MAINNET_ADDRESS
• Add MCV2_BOND_MAINNET_ADDRESS = 0xc5a076cad94176c2996B32d8466Be1cE757FAa27
• Update DEPLOYMENT_BLOCK to mainnet StoryFactory deployment block

Environment

• Document that production must set NEXT_PUBLIC_CHAIN_ID=8453
• Update .env.example if needed

Acceptance Criteria

• npm run typecheck passes
• npm run build succeeds with mainnet chain ID
• Constants correctly switch between testnet/mainnet based on NEXT_PUBLIC_CHAIN_ID

Dependencies

• Blocked by plotlink-contracts#21 (deploy) — need the actual StoryFactory address

Labels

agent/T3