🤖 fix: repair Nix native rebuild tooling

[coadler]

Summary

• Add Python to the Nix dev shell so node-gyp can rebuild Electron native modules.
• Make make rebuild-native recover when a previous failed optional install left node-pty missing from node_modules.
• Harden native-module presence checks and Nix format checking in temporary directories.

Background
This fixes the NixOS native rebuild path where node-gyp first failed without Python and then @electron/rebuild failed with ENOENT for node_modules/node-pty/package.json after the optional dependency was left missing.

Validation

• make fmt-nix-check
• nix develop --command make rebuild-native
• make static-check

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[coadler]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

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