refactor: dev scripts

[asvishnyakov]

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This PR refactors the development scripts.

Key Changes

• Backend scripts moved to uv scripts – pnpm is no longer used to run them.
• Paired scripts for backend and frontend – Both have linting, formatting, and type-checking scripts, with automatic fixes available for the first two
• Unified scripts for CI, git checks & developers – CI and pre-commit hooks now use the same scripts that developers run locally.