docs: fix markdown formatting and clean up duplicate includes

- Fix markdown formatting in include-policy.md
- Remove duplicate header includes in fs.c

Author: ss-o

docs/explanation/include-policy.md

@@ -78,4 +78,4 @@ When `ZPMOD_ANALYSIS` is set the analysis stubs are used instead of the normal g
 - Integrate the checker in CI as a required step.
 - Add a `--fix` mode (optional) for bulk reformatting when large refactors land.
 
-_Last updated: 2025-08-24_
+\_Last updated: **2025-08-24**

src/core/fs.c

@@ -15,11 +15,6 @@
 #include <fcntl.h>
 #include <limits.h>
 #include <sys/stat.h>
-#include <dirent.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <limits.h>
-#include <sys/stat.h>
 #if defined(__has_include)
 #if __has_include(<sys/mman.h>)
 #include <sys/mman.h>