chore: prepare React 17 upgrade (WIP)

[bosun-ai]

Summary

Prepare for upgrading React from 16.8.6 to 17.0.2. This is a work-in-progress test PR with no code changes yet.

Changes

• Add .nvmrc specifying Node.js 12 to align local environment before the upgrade.

Context and Intent

• The goal is to upgrade react from 16.8.6 to 17.0.2. This PR currently sets up environment consistency and serves as a placeholder while upgrade steps are planned and executed.

Impact/Risks

• No functional changes at this time.
• Node version pinning may affect local development environments; developers using nvm will switch to Node 12 automatically in this directory.

Follow-ups / Next Steps

• Update package.json and package-lock.json to bump react and react-dom to 17.0.2.
• Audit and update any peer dependencies and related libraries (e.g., testing libraries, ESLint plugins) that may require compatibility updates.
• Run the application and test suite to identify any breaking changes or warnings.
• Verify build and deployment pipelines for Node 12 compatibility, or consider aligning to a newer supported Node LTS if appropriate.

Reviewer Action Items

• Confirm Node version policy for this repository (is Node 12 intended, or should we target a newer LTS?).
• Share any known constraints or areas likely impacted by React 17 (e.g., legacy lifecycle methods, portals, event handling changes).
• Confirm if CI needs updates to enforce the Node version.

Notes

• This PR is a draft and should not be merged.

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This pull request is created by bosun, a code maintenance automation platform. For more information, visit bosun.ai.