[MEDIUM] Enable no-console ESLint rule with appropriate overrides

[kilodesodiq-arch]

Engineering Gap

ESLint configs lack no-console rule enforcement despite 20+ console.* calls in production code. .eslintrc.js and app/backend/eslint.config.mjs both omit this rule.

Codebase Evidence

• .eslintrc.js: No no-console rule in rules object
• app/backend/eslint.config.mjs: No no-console rule
• app/frontend/eslint.config.mjs: Next.js defaults — may include console warnings

Risk Profile

Current Risk

Gradual accumulation of unstructured console output. Potential data leakage.

Business Impact

Degraded observability. Compliance risk from unredacted console output.

Remediation Strategy

Add no-console as warn in all ESLint configs. Suppress for specific dev-only files (seed scripts, debug helpers). Progress to error after cleanup.

Success Conditions

• no-console rule enabled as warn minimum
• Dev-only files explicitly excluded
• CI lint passes

Change Surface

Files: .eslintrc.js, app/backend/eslint.config.mjs

Security Review

Reduces information leakage through console.

Completion Checklist

• Implementation completed
• Peer reviewed
• Lint passing
• Ready for merge