Rename script/install to script/fetch-policy

By convention, and in scripts-to-rule-them-all, script/install installs
the program itself. This script fetches the shared policy files into a
repo. The make target, the test names and the messages take the new
name. Behaviour is unchanged.

Model: opus-5-5

Makefile

@@ -1,4 +1,4 @@
-.PHONY: bootstrap setup test lint fmt fmt-check check docker hooks install update-policy
+.PHONY: bootstrap setup test lint fmt fmt-check check docker hooks fetch-policy update-policy
 
 # Makefile targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
@@ -31,8 +31,8 @@ docker:
 hooks:
 	@script/install-precommit
 
-install:
-	@script/install
+fetch-policy:
+	@script/fetch-policy
 
 update-policy:
 	@script/update-policy