Validate and bound config request inputs

[mikewheeleer]

Validate config

Description

config inputs aren't fully bounded. This issue adds declarative validation.

Requirements and context

• Repository scope: StableRoute-Org/Stableroute-backend only.
• Validate config request inputs against a schema with sane bounds; reject invalid with structured 400s.
• Behaviour otherwise unchanged.
• Cover valid and invalid in tests.

Suggested execution

• Fork the repo and create a branch
• git checkout -b refactor/config-91-validate
• Implement changes
  • Write code in: the relevant module.
  • Write comprehensive tests in: cover the new behaviour and edge cases.
• Test and commit

Test and commit

• Run npm run lint, npm test, and npm run build.
• Cover edge cases: valid passes, oversized/malformed rejected.
• Include the full test output in the PR description.

Example commit message

refactor(config): validate and bound inputs

Guidelines

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

Community & contribution rewards

• 💬 Join the StableRoute community on Discord: 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 — a 5-star rating is much appreciated.