feat: add CORS validation, environment configuration matrix, config schema validation, and notification compatibility tests

[amanosiadnan-cmyk]

closes #689
closes #693
closes #694
closes #702

PR Description

Summary

Implements the required production architecture and configuration improvements for Notify-Chain:
• #689: Add CORS Configuration Validation (listener/src/utils/cors-validator.ts, listener/src/config.ts)
• #693: Add Environment Configuration Documentation Matrix (docs/ENVIRONMENT_MATRIX.md, ENVIRONMENT_VARIABLES_AND_SECRETS.md)
• #694: Add Configuration Schema Validation (listener/src/config-schema.ts, listener/src/config.ts)
• #702: Add Notification Schema Compatibility Tests (listener/src/tests/notification-schema-compatibility.test.ts)

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Detailed Changes by Issue

1. Add CORS Configuration Validation #689 — Add CORS Configuration Validation
   • Created validateCorsOrigin in listener/src/utils/cors-validator.ts to strictly validate allowed origins during application startup.
   • Validates URI scheme (requiring http: or https:), rejects malformed origins, and prevents trailing path segments.
   • Restricts wildcard origin (*) in production/staging environments, preventing silent fallback to insecure permissive settings.
   • Integrated into validateConfig() in listener/src/config.ts and added comprehensive unit tests in listener/src/utils/cors-validator.test.ts.

2. Add Environment Configuration Documentation Matrix #693 — Add Environment Configuration Documentation Matrix
   • Created a single reference table in docs/ENVIRONMENT_MATRIX.md detailing every supported environment variable, data types, required/optional/conditional status, default values,
   sensitivity levels (Public vs Secret), and applicable environments (Development, Staging, Production).
   • Cross-referenced in docs/LISTENER-CONFIGURATION.md and ENVIRONMENT_VARIABLES_AND_SECRETS.md.

3. Add Configuration Schema Validation #694 — Add Configuration Schema Validation
   • Implemented ConfigurationSchemaValidator in listener/src/config-schema.ts defining explicit type constraints, numeric range limits (e.g. min/max ports, timing bounds), and
   allowed enumerated values.
   • Integrated into validateConfig to ensure all configuration errors pinpoint the exact offending field path (e.g. [scheduler.pollIntervalMs]).
   • Added unit test suite in listener/src/config-schema.test.ts.

4. Add Notification Schema Compatibility Tests #702 — Add Notification Schema Compatibility Tests
   • Added test suite in listener/src/tests/notification-schema-compatibility.test.ts covering consumer payload formats across Discord webhooks, generic webhooks, email, and SMS.
   • Verified backward and forward schema compatibility, version stamping (CURRENT_NOTIFICATION_VERSION = 1), and clear error reporting on schema violations.

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