Fix documentation drift in the visualizer and artwork docs

[kahrendt]

Three documentation defect fixes.

What changed

VisualizerDataType enum table (docs/integration-guide.md)

The table was missing the PEAK row entirely, and described F_PEAK as "Peak frequency" when it carries the dominant frequency and its amplitude (see VisualizerRoleListener::on_f_peak). Row descriptions now match the enum comments in include/sendspin/config.h, and the row order matches declaration order.

VisualizerRole::request_format() (docs/integration-guide.md)

request_format() and its VisualizerFormatRequest struct are public API with no mention anywhere in the guide. Added a snippet in the Visualizer Role section showing a rate-only change and a types change, plus the note that an active stream gets a fresh stream/start (so on_visualizer_stream_start() fires again with the updated config) while an idle server remembers the request for the next stream.

SlotBuffer synchronization (docs/internals.md, "Other Primitives")

The list claimed ArtworkRole::Impl::SlotBuffer::write_idx and drain_active are std::atomic. They are plain uint8_t/bool; every SlotBuffer field is guarded by DrainTask::slot_mutex (see the SlotBuffer doc comment in src/artwork_role_impl.h). Replaced the two false bullets with one mutex bullet covering all the fields it guards.

Notes for reviewers

• Both designated-initializer forms in the new snippet were compile-tested under -std=c++20 against the real VisualizerFormatRequest layout. .types = {{...}} needs the double braces (outer for the optional, inner for the vector); that is what the snippet uses.
• The Visualizer Role intro sentence said "peak frequency"; changed to "dominant-frequency" for consistency with the corrected F_PEAK description.
• The neighboring ArtworkRole::Impl::stream_active bullet was checked and left alone; it is a real std::atomic<bool>.

[Copilot]

🟢 Approval recommended

Changes are documentation-only and the updated statements align with the current public headers and implementation comments for the referenced APIs and synchronization behavior.

Pull request overview

Fixes documentation drift around the Visualizer and Artwork roles so the guides accurately reflect the current public API and synchronization model.

Changes:

• Corrected VisualizerDataType reference table to include PEAK and to describe F_PEAK as frequency + amplitude, matching include/sendspin/config.h.
• Documented VisualizerRole::request_format() usage and clarified stream restart behavior when changing visualizer format at runtime.
• Fixed docs/internals.md to describe ArtworkRole::Impl::SlotBuffer synchronization as mutex-guarded (not atomics), consistent with src/artwork_role_impl.h.

File summaries

File	Description
docs/internals.md	Updates the “Other Primitives” section to accurately describe SlotBuffer synchronization via DrainTask::slot_mutex.
docs/integration-guide.md	Aligns visualizer terminology, documents request_format(), and corrects the VisualizerDataType enum table to match the public headers.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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