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>

tools/check.sh

@@ -1,11 +1,11 @@
 #!/usr/bin/env bash
 # The task gate: every configure preset built, and only then every one tested.
 #
-# The loop itself is libavr's (tools/check-presets.sh) because the order in it
-# is subtle and was got wrong by hand more than once - the mode-identity checks
-# read the sibling mode's tree, so a build-then-test-per-preset run compares a
-# fresh image against a stale sibling. Anything this repository needs beyond
-# the presets is written after the call, where every tree is built and tested.
+# The loop itself is libavr's (tools/check-presets.sh): the mode-identity
+# checks read the sibling mode's tree, so a build-then-test-per-preset run
+# would compare a fresh image against a stale sibling. Anything this repository
+# needs beyond the presets is written after the call, where every tree is built
+# and tested.
 set -euo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")/.."
 "${LIBAVR_ROOT:-libavr}/tools/check-presets.sh" "$@"