Implement all 16 ServiceNow MCP tools

Add complete implementation for all documented tools across 5 categories:

## Core Platform Tools (5 tools):
- query_records: Query with filters, fields, pagination, sorting ✅
- get_table_schema: Get table structure and field information
- get_record: Retrieve specific record by sys_id
- get_user: Look up user by email or username
- get_group: Find assignment group by name or sys_id

## CMDB Tools (3 tools):
- search_cmdb_ci: Search configuration items with queries
- get_cmdb_ci: Get specific CI details
- list_relationships: Show parent/child CI dependencies

## ITOM Tools (5 tools):
- list_discovery_schedules: Check active discovery schedules
- list_mid_servers: Verify MID server health and status
- list_active_events: Monitor infrastructure events
- cmdb_health_dashboard: Get data quality metrics
- service_mapping_summary: Understand service dependencies

## ITSM Tools (1 tool):
- create_change_request: Create change records (write operation)

## Natural Language Tools (2 tools):
- natural_language_search: Query using plain English
- natural_language_update: Update records conversationally (experimental)

## Technical Implementation:
- Added 14 new type interfaces to src/servicenow/types.ts
- Added 15 client methods to ServiceNowClient class
- Added 15 new tool definitions with full schemas
- Implemented input validation for all tools
- Added write-permission checks for write operations
- All tools use existing retry logic and error handling

## Features:
- Full ServiceNow REST API integration
- OAuth and Basic Auth support
- Proper error codes and messages
- MCP protocol compliant responses
- Comprehensive tool descriptions

Total: 16 fully functional tools ready for use

Tested with: https://inteliblissltddemo2.service-now.com

Author: habenani-p