Extract narrow interface for CWService radio dependency

[ny4i]

Problem

CWService depends on RadioController directly. To unit-test CWService, we had to make 3 methods virtual on RadioController (isConnected, setCWSpeed, getCWSpeedRange) and mock via inheritance. This works but:

1. Performance: MockRadioForCW inherits RadioController which starts a worker thread on construction. Even with a shared fixture, the CW test takes 1.52s for 11 trivial tests — almost all of that is thread start/stop overhead.
2. Coupling: CWService only needs 3 methods but inherits the entire RadioController surface area (connect, disconnect, frequency, band, mode, PTT, RIT, XIT, split, etc.).
3. Fragility: Adding new RadioController constructor side effects will silently slow down or break CW tests.

Proposed Fix

Extract a narrow interface:

class ICWRadio {
public:
    virtual ~ICWRadio() = default;
    virtual bool isConnected() const = 0;
    virtual void setCWSpeed(int wpm) = 0;
    virtual void getCWSpeedRange(int& minWpm, int& maxWpm) const = 0;
};

• RadioController implements ICWRadio
• CWService depends on ICWRadio* instead of RadioController*
• Test mock implements ICWRadio directly — no thread, no overhead
• Remove virtual from the 3 RadioController methods (no longer needed)

Current Workaround

Comment in RadioController.h line 42-43 documents the technical debt:

// Note: isConnected, setCWSpeed, getCWSpeedRange are virtual to allow test mocking.
// Ideally CWService would depend on a narrow interface, not RadioController directly.

Shared test fixture in test_cw_service.cpp mitigates the performance issue (6.5s → 1.52s).

Acceptance Criteria

• ICWRadio interface extracted
• CWService depends on ICWRadio*
• RadioController implements ICWRadio
• Test mock implements ICWRadio directly (no thread overhead)
• CW test runs in <0.5s
• virtual removed from RadioController methods