chore(deps): migrate repo TypeScript stack to v6

[alainncls]

Summary

Upgrade the repo TypeScript stack to the latest eligible major versions older than 3 days as of 2026-04-23:

• typescript 5.9.3 -> 6.0.3
• @types/node 22.19.17 -> 25.6.0

This impacts the root config plus contracts, sdk, explorer, and tutorial.

Why this is not in the current dependency bump PR

This is a compiler/tooling major upgrade that can change type-checking, declaration emit, tsconfig expectations, and workspace build behavior.

Documentation

• https://devblogs.microsoft.com/typescript/announcing-typescript-6-0/
• https://devblogs.microsoft.com/typescript/announcing-typescript-6-0-rc/

Expected codebase changes

• Review root and workspace tsconfig files for breaking compiler option behavior.
• Re-check Node typing assumptions across scripts, SDK build tooling, and frontend builds.
• Address any new type errors or declaration output changes.

Migration plan

1. Upgrade TypeScript and Node types together.
2. Run type-check/build flows in every impacted workspace.
3. Fix code or config for any new TS 6 diagnostics.
4. Review generated declaration outputs in packages that publish artifacts.
5. Update CI/editor guidance if a newer TypeScript runtime is required.

Validation checklist

• sdk build
• explorer build
• tutorial build
• contracts tests/build flows that compile TypeScript tooling
• Any root-level lint/typecheck job used in CI

[alainncls]

Pas de PR TypeScript 6 ouverte dans ce passage. La migration compiler doit être isolée de Vite/Solhint/Hardhat pour diagnostiquer proprement les nouveaux types et les éventuels changements de module resolution.