Implement data ring buffer

[malikalhack]

Thread-safe shared buffer connecting capture thread output to render consumption

[malikalhack]

Plan: Data ring buffer (capture → render)

1. WaveformRingBuffer component (capture/inc/waveform_ring_buffer.h + capture/src/waveform_ring_buffer.cpp)

Fixed-capacity, thread-safe buffer of decoded frames (SWaveformSamples + trigger point), mirroring the existing RawPacketQueue style (non-blocking push, drop-oldest overflow with a dropped-frame counter, reset()).
Consumer side is non-blocking popLatest(): drains any backlog and returns only the freshest frame, since a real-time render loop must never block on an empty/stale buffer.
Commit: "Added thread-safe waveform ring buffer".
2. Wire it into acquisition_loop

Replace the current ad hoc single-slot snapshot (waveformMutex / latestWaveform / hasWaveform fields in SAcquisitionLoop) with a WaveformRingBuffer member.
processRawPackets pushes each decoded frame into it; getLatestWaveform() keeps its existing public signature but now delegates to popLatest().
Commit: "Connected acquisition output to the waveform ring buffer".
3. Minimal render-side consumption (main.cpp)

Call getLatestWaveform() once per frame in the render loop and surface it on the status line (e.g. sample count / trigger point) as concrete proof of the capture→render path.
Actual waveform plotting stays out of scope (separate later task).
Commit: "Consumed the latest waveform frame in the render loop".
4. Deterministic tests (tests/waveform_ring_buffer_test.cpp)

FIFO/latest semantics, overflow drop-oldest + dropped-count, reset/reopen, concurrent producer/consumer — same shape as raw_packet_queue_test.cpp.
Register the new test executable/add_test in CMakeLists.txt.
Commit: "Added waveform ring buffer tests".
5. Build/test verification

Debug and Release builds, full CTest run, confirm no new warnings.
6. Documentation

Append a HISTORY.md entry for this stage-4 step.
Update repo memory (/memories/repo/stage3-usb-recovery.md or a new stage4 note) with the design decision (ring buffer scope, why capture-module placement over core/render).