Progress: enforce rule-of-five (currently default copy → double-pop)

[gagelarsen]

Follow-up from issue #116 (review finding #10).

xmscore/misc/Progress.h:23-39 — Progress is documented as an RAII helper that pushes a slot in its ctor and pops it in its dtor, but it leaves the implicit copy ctor / copy-assign generated. A copy duplicates m_stackIndex; both copies pop on destruction → double-pop on the listener stack.

```cpp
class Progress {
public:
Progress(...);
~Progress(); // pops the progress stack
private:
int m_stackIndex; // copyable by default
};
```

Proposed change

Pick one:

1. Delete copy/move (simplest, matches docs):
   ```cpp
   Progress(const Progress&) = delete;
   Progress& operator=(const Progress&) = delete;
   Progress(Progress&&) = delete;
   Progress& operator=(Progress&&) = delete;
   ```
2. Rule-of-zero via pimpl: hold std::unique_ptr<Impl> so the impl owns the stack slot; the implicit special members then do the right thing.

Why follow-up, not part of #117

The new \brief in #117 freezes "RAII helper" as the contract while the type silently breaks it. Picking between (1) and (2) is a real type-design call, not a doc fix.

Acceptance

• Progress cannot be copied (or, if copies are kept, copying does not produce duplicate stack slots)
• Existing call sites still compile (or are migrated)
• CxxTest coverage for the previously-broken double-pop case

Refs: issue #116, PR #117.