fix(core): error handling and typed query for the per-year contributions fetch

[marcalexiei]

• fetchTotalContributions read contribRes.data.data.user without checking for errors.
  Now follows the standard approach: first error message, wrapped for the card, or a generic GRAPHQL_ERROR.
• The runtime-built contributions query is typed end to end:
  the new graphql/contributionsDocument.ts assembles the per-year aliases around ...YearContributions spreads (typed by the fragment in stats.graphql).
  It is sent via createGraphQLFetcher, the untyped request call and its cast are gone.

[vercel]

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