fix: parse activation response root element correctly

[Edgars-Ralfs-Dunis]

Problem

Activate returns success: true, messages: [] even when SAP rejects the activation — the object silently stays inactive. Every workflow that trusts activation.Success (WriteSource, WriteClass, DeployFromFile, CreateTable, ActivatePackage — ~20 call sites) inherits the false positive. Verified on v2.38.1 and current main.

Repro: write a program with a syntax error via UpdateSource (so the pre-save check doesn't block), call Activate → {"success": true, "messages": []}, but GetInactiveObjects shows the object still inactive.

Root cause

Replaying the activation POST with curl shows SAP does return the error — HTTP 200 with:

<chkl:messages xmlns:chkl="http://www.sap.com/abapxml/checklist">
  <msg objDescr="Program Z_ACT_TEST" type="E" line="1"
       href="/sap/bc/adt/programs/programs/z_act_test/source/main#start=2,6" forceSupported="true">
    <shortText><txt>Field "LV_UNDEFINED_VARIABLE" is unknown.</txt></shortText>
  </msg>
</chkl:messages>

parseActivationResult declares messages/inactiveObjects as child fields, but <chkl:messages> (or <ioc:inactiveObjects>) is the root element. xml.Unmarshal maps the root onto the target struct itself, so the parser looked for a <messages> child inside the root, matched nothing, decoded zero messages without error, and Success stayed true. (The sibling parseSyntaxCheckResults declares its structs one level deeper, which is why SyntaxCheck works.)

Fix

Declare the root's children (<msg> / <entry>) directly on the response struct — both known root forms parse with one struct since unmarshalling matches child local names.

Testing

• New regression tests in pkg/adt/devtools_activation_test.go using a real payload captured from a NW 7.50 system: error-message root form, inactive-objects root form, empty-body success.
• Red/green verified: all three tests fail against the previous parser, pass with the fix.
• go vet ./pkg/adt clean.