chore: bump version to 2.8.3 and update changelog

- Updated version in package.json and package.runtime.json
- Updated version badge in README.md
- Added comprehensive changelog entry for v2.8.3
- Fixed TypeScript lint errors in test files by making env vars optional
- Fixed edge-cases test to include required NODE_ENV

🤖 Generated with [Claude Code](https://claude.ai/code)

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

types/test-env.d.ts

@@ -11,14 +11,14 @@ declare global {
       TEST_ENVIRONMENT?: string;
 
       // Database Configuration
-      NODE_DB_PATH: string;
+      NODE_DB_PATH?: string;
       REBUILD_ON_START?: string;
       TEST_SEED_DATABASE?: string;
       TEST_SEED_TEMPLATES?: string;
 
       // API Configuration
-      N8N_API_URL: string;
-      N8N_API_KEY: string;
+      N8N_API_URL?: string;
+      N8N_API_KEY?: string;
       N8N_WEBHOOK_BASE_URL?: string;
       N8N_WEBHOOK_TEST_URL?: string;