[MCP] Allow admin to define the default configuration

[onbuyuka]

Summary

Adds the ability for administrators to designate an MCP configuration as the default. When no configuration is specified by an MCP client connection, the designated default configuration is used instead of the built-in system default.

Changes

Public API (MCPConfig.Codeunit.al)

• SetAsDefaultConfiguration(ConfigId: Guid) — designates a configuration as default (must be active)
• ClearDefaultConfiguration() — clears the current default and restores the system default (Name = '')

Implementation (MCPConfigImplementation.Codeunit.al)

• SetAsDefaultConfiguration — clears all existing defaults via ModifyAll, sets the new one, emits telemetry
• ClearDefaultConfiguration — clears non-system defaults, re-marks the system default
• IsDesignatedDefaultConfiguration — reads the native Default Boolean field
• MarkSystemDefaultAsDefault — local helper to restore system default
• CreateDefaultConfiguration — sets Default := true on initial system default creation
• CopyConfiguration — ensures copies are created with Default := false
• DeleteConfiguration — if deleting the designated default, restores system default first
• ActivateConfiguration — prevents deactivation of the designated default
• GetDimensions — includes IsDesignatedDefault in telemetry

Pages

• MCPConfigCard.Page.al — Default field (read-only), Set as Default / Clear Default promoted actions, deactivation guard on Active field OnValidate
• MCPConfigList.Page.al — Default column, Set as Default / Clear Default actions in Advanced group

Upgrade (MCPUpgrade.Codeunit.al)

• UpgradeMCPSystemDefaultAsDefault — marks existing system default record (Name = '') as Default := true on upgrade (tag: MS-612454-MCPSystemDefaultAsDefault-20260216)

Tests (MCPConfigTest.Codeunit.al)

• TestSetAsDefaultConfiguration — setting default clears system default
• TestClearDefaultConfiguration — clearing restores system default
• TestOnlyOneDefaultConfiguration — only one configuration can be default at a time
• TestCopyConfigurationDoesNotCopyDefault — copies don't inherit default flag
• TestCannotSetInactiveConfigurationAsDefault — inactive configs cannot be default
• TestCannotDeactivateDesignatedDefault — designated default cannot be deactivated
• TestDeleteDesignatedDefaultRestoresSystemDefault — deleting default restores system default

Design decisions

• The Default field is a native Boolean on the platform MCP Configuration table — no table extension needed
• System default (Name = '') starts with Default = true; any config can be designated as default
• At most one configuration has Default = true at any time
• Clearing the default is generic (parameterless) — always reverts to the system default
• Deactivation of the designated default is blocked on both the codeunit and card page levels

Fixes AB#612454