Initial commit: Chatter — assistive-writing app for reMarkable Paper Pro Move

Direct-framebuffer ink pipeline (stock-quality strokes), finger-wipe erase,
growable scrolling canvas with color-ghost cleanup, bidirectional toggle with a
persistent 4-finger return launcher, instant button feedback. Includes prebuilt
aarch64 binaries (dist/), build/deploy/install scripts, a user guide, and a
complete technical reference.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/grabtest.c

@@ -0,0 +1,26 @@
+// Probe whether an input device is exclusively grabbed (EVIOCGRAB) by another
+// process (e.g. xochitl). If we can grab it, it was free -> a background watcher
+// can read it alongside xochitl. If EBUSY, xochitl holds it exclusively.
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/input.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+
+int main(int argc, char **argv)
+{
+    const char *dev = argc > 1 ? argv[1] : "/dev/input/event3";
+    int fd = open(dev, O_RDONLY);
+    if (fd < 0) { printf("%s: open failed: %s\n", dev, strerror(errno)); return 1; }
+    int r = ioctl(fd, EVIOCGRAB, (void *)1);
+    if (r == 0) {
+        ioctl(fd, EVIOCGRAB, (void *)0); // release immediately
+        printf("%s: NOT exclusively grabbed -> a watcher can read it\n", dev);
+    } else {
+        printf("%s: GRABBED by another process (%s)\n", dev, strerror(errno));
+    }
+    close(fd);
+    return 0;
+}