chore: the editor reads the selected preset's database, and the config states no history

clangd's database is the one CMake Tools copies from the selected preset,
as in libavr, rather than one chip's tree. .gitattributes drops two Studio
patterns nothing here matches, .clangd is ASCII, and the comments in it,
check.sh and .gitattributes state the reason without the account of how it
was found.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitattributes

@@ -1,12 +1,8 @@
-# Line endings are the repository's, not the editing machine's: this checkout
-# is reached from two hosts, and a file rewritten by a Windows tool comes back
-# with every line changed unless something says otherwise. Naming the source
-# extensions left Markdown, Python, shell and CMake to whatever the writing
-# tool defaulted to, which is CRLF on one of the two.
+# Line endings are the repository's, not the editing tool's (libavr guidance
+# rule 50): a file rewritten by a Windows tool must not come back with every
+# line changed.
 * text=auto eol=lf
 
 # Atmel Studio writes these and expects them back.
-*.vcxproj*  eol=crlf
 *.cppproj   eol=crlf
-*.sln       eol=crlf
 *.atsln     eol=crlf