Clean up common/ comments and the log-ring strncpy warning

Comments must not document the past or reference plan circumstances:
drop the stale pointer to a never-created audio_correlate_layout.hpp,
the "step b" plan labels, the "carved out of reserved space" history
note, and a README pointer; reword a past-tense seqlock comment to
describe the failure mode in the present.

Replace the strncpy in log_ring_push with a bounded memcpy: same
semantics (truncate + NUL), but without the C4996 deprecation warning
on every host build.

common/include/coop/tone_analysis.hpp

@@ -11,7 +11,7 @@
 //
 // Header-only, no Windows / no audio-device dependency, so it is unit-tested with
 // synthesized adversarial signals (tests/tone_analysis_test.cpp) and reused by the
-// coop_audio_validate tool. See README "Lessons learned" / the audio notes.
+// coop_audio_validate tool.
 #pragma once
 
 #include <algorithm>