feat: add lightweight staged-file pre-commit gates

[google-labs-jules]

Context & Rationale

Currently, developers can push poorly formatted or style-violating code to remote branches. This shifts the burden of formatting and basic lint checks entirely onto the late-stage CI pipeline, resulting in slower feedback loops and wasted CI resources.

To solve this, we are introducing a lightweight, local pre-commit gate system. By shifting these checks "left" into the local development workflow, we validate compliance before the code ever leaves the developer's machine.

Key Decisions

• Staged-File Targeting: To keep the pre-commit gate fast (under the 3-second target) and avoid forcing developers to refactor untouched legacy code, we use lint-staged. This ensures only newly modified files are validated.
• Tooling Exclusions: We have explicitly excluded full-workspace type-checking and unit-testing from this pre-commit hook to maintain high developer velocity and avoid sluggish commit operations.
• Bun Integration: In alignment with our workspace toolchain, all package scripts and hook initializations are managed via bun.

Proposed Changes

1. Dependency Additions

   • Added husky and lint-staged as development dependencies to orchestrate the Git hook lifecycle.

2. Husky Hook Configuration

   • Added a "prepare": "husky" script in package.json so that Git hooks are automatically registered on developers' local machines upon running bun install.
   • Created a .husky/pre-commit hook that triggers bun x lint-staged whenever a commit is initiated.

3. Staged Validation Configuration

   • Configured lint-staged within package.json to handle staged files:
     • Prettier (prettier --write): Automatically reformats and re-stages files with minor stylistic issues without halting the commit.
     • ESLint (eslint): Scans for code quality violations. If errors are found, the commit is aborted, and the offending lines are outputted directly to the terminal for local remediation.

Verification & Testing

• Successful Commit: Verified that committing fully compliant files passes checks in under 2 seconds.
• Auto-formatting: Verified that committing poorly formatted files triggers Prettier, auto-formats them, re-stages them, and successfully completes the commit.
• Lint Failure Block: Verified that committing files with ESLint errors halts the commit and prints error details.
• Bypassability: Verified that hooks can be safely bypassed when emergency overrides are needed using git commit --no-verify.