feat: separate env

[tianzhou]

Fix #96

[Copilot]

Pull Request Overview

This PR adds support for individual database connection parameters as an alternative to DSN configuration, allowing users to avoid URL encoding issues with special characters in passwords.

• Added buildDSNFromEnvParams() function to construct DSNs from individual environment variables
• Integrated individual parameter support into the existing resolveDSN() function with proper priority handling
• Updated documentation and configuration examples to explain both connection methods

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/config/env.ts	Added new function to build DSN from individual env vars and integrated it into DSN resolution flow
src/config/tests/env.test.ts	Comprehensive test suite covering all database types, edge cases, and integration scenarios
README.md	Updated documentation to explain both DSN and individual parameter methods with examples
.env.example	Added commented examples showing individual parameter configuration options

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