Update high-risk dependencies #436

User story / Problem statement

Currently, core build and runtime dependencies (vite, typescript, zod, graphql-codegen) are one or more major versions behind. These affect the build pipeline, type system, environment validation, and code generation.

Expected outcome

All high-risk dependencies are updated. The build pipeline, type checking, env validation, and code generation work correctly with the new versions.

Acceptance criteria

• All listed packages updated
• vite 8: Build pipeline functional, dev server works, all plugins compatible
• typescript 6: tsc --noEmit passes, no new type errors introduced
• zod 4: Environment validation in src/env.ts works correctly, @t3-oss/env-core compatible
• graphql-codegen 6: pnpm subgraph-codegen produces valid output (if subgraph vars configured)
• pnpm lint && pnpm test && pnpm build pass
• Manual smoke test: dev server starts, app loads, wallet connects, contract interactions succeed

Technical notes

Part of #432. See #432 for branching strategy. Should be done after medium-risk dependencies (#435) land.

Branch: TBD (sub-branch off chore/update-medium-risk-deps or whichever branch is current after #435 merges)
PR: TBD (targets the branch from #435)