chore: prepare React upgrade to 17.0.2 (WIP)

[bosun-ai]

Work in progress: React upgrade from 16.8.6 to 17.0.2

Scope

• This PR is intended to upgrade the frontend React dependency from 16.8.6 to 17.0.2.
• At this stage, the repository shows changes only to yarn.lock, indicating dependency resolution updates without corresponding package.json or source changes.

Reasoning

• Aligning the project with React 17.0.2 to take advantage of maintenance and compatibility updates. No new features are introduced by React 17, but it adjusts event system behavior and improves compatibility with concurrent React versions.

Current State

• No modifications to package.json or application source code were detected in this branch; only yarn.lock differs from main.
• Additional updates are expected to ensure package.json reflects the React and react-dom versions, and to validate compatibility across the app.

Impact/Risks

• Upgrading React may affect:
  • Event delegation changes in React 17 (root-level event listeners attached to the root container instead of document) which could impact custom listeners or integrations.
  • Third-party libraries that rely on React internals or specific lifecycle behaviors.
  • Flow-typed/react type stubs currently reference v16; these may require updating.

Follow-ups / Reviewer call-outs

• Confirm that package.json has react and react-dom updated to 17.0.2; currently not reflected in the diff.
• Audit and update flow-typed definitions (e.g., flow-typed/npm/react_v16.8.0.js) to React 17 equivalents as needed.
• Run the application and test suite to identify any regressions related to event handling, portals, and error boundaries.
• Verify compatibility of tooling (react-scripts, babel, eslint-plugin-react, react-router) with React 17.
• If the upgrade is intended to be lockfile-only, document the rationale; otherwise, ensure package.json is updated and add migration notes.

This is a test PR and should not be merged. This PR is a work in progress.

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