Rename power.h to Power.h for casing consistency with Power.cpp (#10919)

Every other .cpp/.h pair in src/ (350 of 351) uses identical
capitalization between the two files. Power.cpp/power.h was the sole
outlier; this aligns it with the rest of the codebase. No functional
change — all includes already resolved this file the same way on
case-sensitive filesystems.

Assisted-by: Claude Sonnet 5 <noreply@anthropic.com>

Signed-off-by: Andrew Yong <me@ndoo.sg>
Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

variants/nrf52840/ELECROW-ThinkNode-M6/variant.cpp

@@ -19,8 +19,8 @@
 */
 
 #include "variant.h"
+#include "Power.h"
 #include "nrf.h"
-#include "power.h"
 #include "wiring_constants.h"
 #include "wiring_digital.h"