Add an ESLint config and run lint in CI

[mikewheeleer]

Implement an ESLint config and enforce it in CI

Description

package.json defines "lint": "eslint src --ext .ts" and depends on eslint@^9, but there is no ESLint config file in the repo, so npm run lint cannot run with a working ruleset, and .github/workflows/ci.yml never invokes lint. This issue adds a flat-config ESLint setup with TypeScript support and gates CI on it.

Requirements and context

• Repository scope: StableRoute-Org/Stableroute-backend only.
• Create eslint.config.js (create file) using ESLint 9 flat config with typescript-eslint, targeting src/**/*.ts.
• Add @typescript-eslint/parser and typescript-eslint (or @typescript-eslint/eslint-plugin) to devDependencies.
• Enable a sensible ruleset (recommended + no-floating-promises once type-aware linting is configured) and fix or // eslint-disable justified violations.
• Add a Lint step to .github/workflows/ci.yml running npm run lint.

Suggested execution

• Fork the repo and create a branch
• git checkout -b enhancement/tooling-25-eslint-config
• Implement changes
  • Write code in: create eslint.config.js; update package.json and .github/workflows/ci.yml.
  • Write comprehensive tests in: n/a — CI lint step is the gate; ensure npm test still passes.
  • Add documentation: note the lint workflow in README.md.
  • Validate security: enable rules that catch unsafe any and floating promises.
• Test and commit

Test and commit

• Run npm run lint, npm run build, and npm test — all must pass clean.
• Cover edge cases: lint fails on an intentionally bad sample, passes on src/.
• Paste npm run lint output in the PR.

Example commit message

chore(tooling): add ESLint flat config and enforce lint in CI

Guidelines

• Minimum 95 percent test coverage for impacted code.
• Clear, reviewer-focused documentation.
• Timeframe: 96 hours.

Community & contribution rewards

• 💬 Join the StableRoute community on Discord for questions, reviews, and faster merges: https://discord.gg/37aCpusvx
• ⭐ This is a GrantFox OSS / Official Campaign task and may be rewarded. When your PR is merged you'll be prompted to rate the project — if this issue and the maintainers helped you ship, we'd be grateful for a 5-star rating. Clear questions in Discord and tidy, well-tested PRs are the fastest path to a merge and a reward.