🐛 Bug-fix PR

Closes #2348

📌 Summary

Fixed an issue where invalid JSON schemas for tools and prompts were being silently persisted with only a warning log, leading to potential runtime errors in downstream components.

Key Changes:

1. Strict Validation: processing is now halted when an invalid schema is detected. This prevents broken data(json) from entering the database.
2. MCP Spec Compliance: The default JSON Schema version for payloads missing the $schema field is now explicitly set to Draft 2020-12, as mandated by the MCP Schema Specification.
3. Configuration: A new setting JSON_SCHEMA_VALIDATION_STRICT has been added (defaults to True) to control this behavior, with valid documentation.

🔁 Reproduction Steps

1. Attempt to register a tool or prompt with a syntactically invalid JSON schema (e.g., {"type": "object", "properties": {"p": {"type": "UNKNOWN_TYPE"}}}).
2. Before: Request succeeds (200 OK), and a warning is logged.
3. After: Request fails (400 Bad Request) with a clear error message: Invalid tool input schema: ....

🐞 Root Cause

1. Swallowed Exceptions: The validate_tool_schema and validate_prompt_schema database listeners caught jsonschema.exceptions.SchemaError but effectively ignored it by only logging a warning and allowing the transaction to commit.
2. Ambiguous Default: The validator selection logic did not explicitly enforce the MCP-required default (Draft 2020-12) for schemaless inputs, leading to potential inconsistencies.

💡 Fix Description

• Config: Introduced json_schema_validation_strict in Settings to allow opting out of strict mode (for legacy compatibility).
• Logic: Updated mcpgateway/db.py to:
  • Check settings.json_schema_validation_strict. If True, SchemaError is caught and re-raised as ValueError, aborting the DB transaction.
  • Explicitly instantiate jsonschema.Draft202012Validator if $schema is missing.
• Tests: Added reproduction tests verifying both strict and lenient behaviors, and confirming the default validator version.

Note on Configuration: JSON_SCHEMA_VALIDATION_STRICT is distinct from the existing VALIDATION_STRICT setting.

• VALIDATION_STRICT: Controls general API input validation (middleware level) for request bodies/parameters.
• JSON_SCHEMA_VALIDATION_STRICT: Specifically controls whether invalid JSON Schemas (defined inside Tool/Prompt inputs) cause a hard failure/exception during registration or are just logged as warnings.

🧪 Verification

📐 MCP Compliance (if relevant)

• Matches current MCP spec
• No breaking change to MCP clients

✅ Checklist

• Code formatted (make black isort pre-commit)
• No secrets/credentials committed