feat(hub): add vp_value query to get total vp value

[wa0x6e]

Adds a vp_value query to the hub GraphQL API returning a voter's total monetary voting-power value, broken down by space.

Port of snapshot-labs/snapshot-hub#1066 to the monorepo's apps/hub.

Changes

• New resolver apps/hub/src/graphql/operations/vpValue.ts (sums votes.vp_value per space for a voter)
• Registered as vp_value in operations/index.ts
• Schema: vp_value(voter: String!): VpValue query + VpValue / VpValueSpace types
• schema.sql: add vp_value column to votes, set scores_total_value to DECIMAL(13,3)

Test plan

query {
  vp_value(voter: "0x...") {
    user
    totalVpValue
    spaces { id totalVpValue }
  }
}