build: git-hooks - Add ESLint validation #393

Build Summary

Add check-only JavaScript/TypeScript linting suited to this React/Vite repository. Coordinate root tooling configuration with existing governance work; no unrelated repository-wide cleanup.

Acceptance Criteria

• Dependencies, configuration, coverage, exclusions and baseline agreed first.
• Relevant changed JS/TS/TSX files checked before commit.
• Invalid code produces actionable failure.
• No autofixes or staging.
• Generated/vendor files excluded.

Definition of Ready

• Scope, fixtures, prerequisites and overlap identified.

Definition of Done

• Criteria pass; commands, revision, environment and exit codes recorded.
• Documentation reflects tests; applicable review/checks pass.

Branch instructions

Recheck repository instructions, active work and PR template; independently reviewable branch from develop; no automatic merged-branch reuse. Preserve unrelated changes; no force-push, merge or deployment. Estimate unset; no dates/milestone.