refactor(call): use typed MCP errors instead of string parsing

[appcypher]

Summary

• Replace string-based error detection with proper typed error handling for MCP service errors
• Preserve structured error information (code, message, data) instead of flattening to strings
• Enables better error messages by accessing typed fields like JSON-RPC error codes
• Fixes issue where "missing field" errors from serde weren't being detected

Changes

• lib/error.rs: Add ToolError::Mcp variant wrapping rmcp::service::ServiceError
• lib/suggest.rs: Add McpErrorKind enum and analyze_mcp_error() function for structured error analysis
• lib/suggest.rs: Add extract_missing_field_from_message() to handle both serde and custom error formats
• lib/suggest.rs: Update is_missing_param_error() to detect serde "missing field" format
• lib/mcp.rs: Simplify call_tool() to propagate typed errors via ? operator instead of stringifying
• lib/handlers/tool/call.rs: Pattern match on ToolError::Mcp and use McpErrorKind for dispatch

Test Plan

• Run cargo build to verify compilation
• Run cargo clippy to check for warnings
• Test with a tool that requires parameters: tool call <tool> -m <method> without required params
• Verify error output shows the missing parameter name and lists required/optional parameters from schema