ROCK-8328: Fix Manage Medications to use camp-specific GroupMember matrix

[jwakefield-secc]

Summary

• Fixed the Manage Medications modal to read/write from the camp-specific GroupMember matrix instead of the Person-level master medication list
• Each camp registration creates its own medication matrix copy via the "Medication Information Request" workflow — edits from the camp medication page should be scoped to that copy
• Previously, adding or deleting medications from the Manage Medications modal would modify the Person's global medication list, affecting all camps

What Changed

• ManageMeds_Click now traces the matrix GUID from the clicked row's AttributeMatrixItemId → AttributeMatrix.Guid instead of querying Person → AttributeValue → matrix GUID
• The downstream handlers (mdAddMedication_SaveClick, btnDeleteMed_Click) already use hfManageMedsMatrixGuid so they automatically work with the correct camp-specific matrix

Data Model Context

• Person attribute (Medications, ID 67024): Master medication list on the Person entity
• GroupMember attribute (Medications, ID 43299+): Camp-specific copy created per registration by workflow type 162 ("Medication Information Request")
• The workflow's AttributeMatrixCopy action copies the Person matrix into a new matrix on the GroupMember at registration time

Test Plan

• Open Medication Manager for a camp group
• Click the pills icon (Manage) on a person's medication row
• Verify the modal shows medications from the camp-specific matrix, not the Person's master list
• Add a medication via the modal — verify it only appears in this camp's context
• Delete a medication via the modal — verify the Person's master medication list is unchanged
• Verify the main grid still displays and distributes correctly after modal changes