Add additional ESLint rules for code quality and consistency

General rules (all files):
- eqeqeq: enforce === instead of ==
- prefer-const: prefer const over let
- no-console: discourage console.log, use logger

TypeScript rules (.ts, .tsx):
- ban-ts-comment: require description for @ts-ignore (min 10 chars)
- no-non-null-assertion: discourage ! operator
- no-unused-vars: detect unused variables (ignore _prefixed)
- naming-convention: enforce camelCase for variables/functions,
  PascalCase for types, with flexibility for API responses

All rules set to 'warn' for gradual adoption.

Refs #72

🤖 Generated with [Claude Code](https://claude.com/claude-code

)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>