deps: the libavr pin advances, and this repository gets a committed gate

The pin moves to libavr's USI I2C rate fix and to the two override surfaces the
fan-controller port filed - a PWM solve that can be pinned, and a capture edge
that is a value rather than a template argument. Nothing here names any of
them; four presets green and no image moved.

`tools/check.sh` is new, and its absence was the defect: this repository had no
committed gate at all, so "run the suite" was a snippet somebody remembered -
and the order in a snippet is the one thing nobody re-derives. Every preset
built before any is tested is subtle and load-bearing, because the
mode-identity check reads the sibling mode's tree and a build-then-test-per-
preset run holds a fresh image against a stale sibling. The loop is libavr's
`tools/check-presets.sh`; nothing is written after the call, there being nothing
beyond the presets this repository knows to ask.

And `.vscode/settings.json` stops naming a toolchain prefix. It named
`D:/dev/libavr/local/toolchain/avr-gcc-16.1.0-mingw`: a path true of one machine
(libavr guidance rule 50) and, since the in-repo toolchain copies went, true of
none. `local/machine.cmake` is where a checkout says that, and it already did.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.vscode/settings.json

@@ -14,14 +14,13 @@
 		"--header-insertion=never"
 	],
 
-	// The presets are the build interface; the toolchain file inside the
-	// libavr submodule is the one place the compiler is chosen. The submodule
-	// carries no local/toolchain for it to discover, so the prefix is named
-	// here, for the window that opens this folder.
+	// The presets are the build interface, and the toolchain file inside the
+	// libavr submodule is the one place the compiler is chosen. **No prefix is
+	// named here**: a committed file may not name a path that is true of one
+	// machine (libavr guidance rule 50), so the gitignored local/machine.cmake
+	// at this repository's root is where a checkout says where its toolchain
+	// is - one file, and it answers for both hosts.
 	"cmake.useCMakePresets": "always",
-	"cmake.environment": {
-		"LIBAVR_TOOLCHAIN": "D:/dev/libavr/local/toolchain/avr-gcc-16.1.0-mingw"
-	},
 	"cmake.configureOnOpen": true,
 	"cmake.options.statusBarVisibility": "compact",
 

tools/check.sh

@@ -0,0 +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.
+set -euo pipefail
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+"${LIBAVR_ROOT:-libavr}/tools/check-presets.sh" "$@"