feat(xh): add 3rd party fallback completion loader

https://github.com/ducaale/xh/blob/d9df32e2e32fa900e4d4003cf87ac880e872508e/doc/xh.1.md?plain=1#L276

Author: scop

completions-fallback/.gitignore

@@ -233,6 +233,7 @@
 /watchexec.bash
 /waydroid.bash
 /xc.bash
+/xh.bash
 /ytt.bash
 /zarf.bash
 /zed.bash

completions-fallback/Makefile.am

@@ -320,6 +320,7 @@ CLEANFILES = \
 	watchexec.bash \
 	waydroid.bash \
 	xc.bash \
+	xh.bash \
 	ytt.bash \
 	zarf.bash \
 	zed.bash \
@@ -557,6 +558,8 @@ symlinks: $(DATA)
 		pip3
 	$(ss) pipenv \
 		black blackd flask httpx
+	$(ss) rg \
+		xh
 	$(ss) ruff \
 		mado \
 		uv \