feat: update configuration for OpenAI and Anthropic endpoints

- Created a new .env.example file with default environment variables for PORT, OPENAI_UPSTREAM_URL, ANTHROPIC_UPSTREAM_URL, and DATABASE_URL.
- Updated .npmignore to exclude all .env files except .env.example.
- Revised CONTRIBUTING.md to simplify the contribution process and provide clearer setup instructions.
- Enhanced cost.ts with detailed type definitions and improved cost calculation logic.
- Updated proxy.ts to include new environment variables and improved logging functionality.
- Modified README.md to reflect new configuration instructions and usage examples.
- Removed unnecessary dashboard files and streamlined the project structure.

.env.example

@@ -0,0 +1,4 @@
+PORT=3007
+OPENAI_UPSTREAM_URL=https://api.z.ai/api/coding/paas/v4
+ANTHROPIC_UPSTREAM_URL=https://api.z.ai/api/anthropic/v1
+DATABASE_URL=postgresql://user:password@localhost:5432/database