refactor: Major code quality improvements and bug fixes

[Abourass]

• Change Node engine constraint to >=25
• Fix critical rule assignment bugs where entire rules object was assigned instead of filtered rules
• Fix disabled rules merging to properly append instead of replace
• Remove duplicate @typescript-eslint/no-var-requires from disabled rules list
• Remove browserslist config (not applicable for Node.js package)
• Replace console.info with proper LintGolemError throwing in init() method
• Refactor to use static readonly constants for all default rules
• Make all instance properties readonly to reduce mutable state
• Add comprehensive validation:
  • Validate rootDir exists and is a directory
  • Validate all tsconfigPaths files exist
  • Validate ecmaVersion values
• Add new validation tests
• Update test suite to use real paths instead of fake paths
• Remove unused eslint-disable directives

All tests passing (23 tests, 90.9% coverage)
All linting and type-checking passing

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	90.9% ⬇️ -6.63%	80 / 88
🔵	Statements	90.9% ⬇️ -6.12%	80 / 88
🔵	Functions	100% 🟰 ±0%	14 / 14
🔵	Branches	75.36% ⬇️ -3.88%	52 / 69

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/LintGolemError.ts	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%
src/index.ts	90.36% ⬇️ -6.51%	75.36% ⬇️ -3.88%	100% 🟰 ±0%	90.36% ⬇️ -7.00%	216-220, 233-237, 242-246, 374, 377, 414-418, 423-427, 453-460

Generated in workflow #27 for commit 2e2aaf9 by the Vitest Coverage Report Action