Repair foot.ini configs holding a literal \n[text-bindings] line (#6938)

A 3.8.3 migration appended the section header with one backslash too many, so
sed wrote the literal characters instead of a newline plus the header. foot
rejects the line and stops reading the rest of the file. The later text-binding
migration matches the header with grep -qxF, misses the broken line, and appends
a second section, leaving the config broken across the Quattro upgrade.

Closes #6903

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
(cherry picked from commit b5bb8dac05)

migrations/1786782461.sh

@@ -0,0 +1,18 @@
+echo "Remove the literal \\n[text-bindings] line an earlier migration wrote into foot.ini"
+
+# A 3.8.3 migration appended the section header with `sed -i '$a\\\n[text-bindings]'`,
+# one backslash too many, so GNU sed wrote a backslash and an "n" as two ordinary
+# characters ahead of the section name, leaving the single line \n[text-bindings]
+# where a blank line and a [text-bindings] header belong. foot rejects it with
+# "syntax error: key/value pair has no value" and stops reading the rest of the file.
+#
+# The later text-binding migration looks for the header with `grep -qxF`, which the
+# literal line doesn't match, so it appends a second real [text-bindings] section and
+# leaves the broken line in place. Removing the line is what actually repairs the
+# config; the duplicate section that migration added is valid and harmless.
+
+foot_config="$HOME/.config/foot/foot.ini"
+
+if [[ -f $foot_config ]] && grep -qxF '\n[text-bindings]' "$foot_config"; then
+  sed -i '/^\\n\[text-bindings\]$/d' "$foot_config"
+fi