Keep the curve and thermistor comments timeless

Both headers described the port transformation ("legacy cubic becomes",
"no hand-rolled series needed") rather than what the code is. State the
cubic and the __builtin_log rationale directly.

Co-Authored-By: Claude <noreply@anthropic.com>

src/curve.hpp

@@ -5,9 +5,9 @@
 
 #include <libavr/flash.hpp>
 
-// The auto-mode fan curve, tabulated at compile time: the legacy cubic
-// (0.002246·x³ − 0.09·x² + 0.91·x, zero below 20 °C) becomes a libavr
-// flash_table of duty percent per °C.
+// The auto-mode fan curve, tabulated at compile time: a cubic in °C
+// (0.002246·x³ − 0.09·x² + 0.91·x, zero below 20 °C) as a flash_table of
+// duty percent per °C.
 namespace app::curve {
 
 namespace detail {