Enforce strict Azure MCP tool-name matching and document snapshot convention

[Copilot]

This updates the Azure MCP reference validation to align with review feedback: keep matching strict and make the convention explicit for skill authors. Tool references in skill markdown are now validated against exact snapshot tool names (with the existing legacy alias), not compound suffix forms.

• Validation behavior

  • Removed permissive prefix acceptance in tests/mcp-tool-references/unit.test.ts.
  • mcp_azure_mcp_<name> references must resolve to an exact toolNames entry (or configured alias).

• Snapshot contract

  • Added toolReferenceConvention to tests/fixtures/azure-mcp-tool-names.snapshot.json to document the rule:
    • exact matches required
    • compound forms like <toolName>_* are unsupported

• Snapshot generation parity

  • Updated tests/scripts/update-mcp-tool-snapshot.js so regenerated snapshots always include the same toolReferenceConvention header.
  • Extended snapshot shape assertions to require the convention field/value.

// Before: accepted compound forms
resolvedToolName.startsWith(`${snapshotToolName}_`)

// After: strict exact-name validation only
if (validToolNames.has(resolvedToolName)) {
  continue;
}