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

prompts/REPO_POLICIES.md

@@ -110,7 +110,7 @@ style conventions are in separate documents:
     - `script/fmt-check`
     - `script/check`
     - `script/docker`
-    - `script/install`
+    - `script/fetch-policy`
     - `script/update-policy`
 
     The scripts must be POSIX sh (`#!/bin/sh`, `set -eu`, no bashisms) so they
@@ -191,10 +191,10 @@ style conventions are in separate documents:
       `script/check`.
     - `script/install-precommit` installs the git pre-commit hook. The
       `make hooks` target shims to it.
-    - `script/install` fetches the vendored policy files from the `prompts` repo
-      over HTTP and writes them into the repo it is given, or its own repo with
-      no argument.
-    - `script/update-policy` fetches the current `script/install` from the
+    - `script/fetch-policy` fetches the vendored policy files from the `prompts`
+      repo over HTTP and writes them into the repo it is given, or its own repo
+      with no argument.
+    - `script/update-policy` fetches the current `script/fetch-policy` from the
       `prompts` repo, runs it on its own repo and commits the result. It does
       not push. The `make update-policy` target shims to it.
     - `script/projectname` (literally that filename) simply outputs the
@@ -937,19 +937,19 @@ style conventions are in separate documents:
   feature branch.
 
 - One command brings a repo up to standards: `make update-policy`. It runs
-  `script/update-policy`, which fetches the current `script/install` from the
-  head of `main` in the `prompts` repo and runs it on the repo. It then commits
-  the files that changed and does not push, so a person reviews and pushes the
-  commit.
+  `script/update-policy`, which fetches the current `script/fetch-policy` from
+  the head of `main` in the `prompts` repo and runs it on the repo. It then
+  commits the files that changed and does not push, so a person reviews and
+  pushes the commit.
 
-    `script/install` fetches each vendored file from `prompts` over HTTP and
-    writes it into the repo. It skips a language's files when git tracks no
+    `script/fetch-policy` fetches each vendored file from `prompts` over HTTP
+    and writes it into the repo. It skips a language's files when git tracks no
     source file of that language. A file the repo lacks is written whole. A
     `prompts/NAME.md` goes to `docs/NAME.md`, unless the repo keeps it at
-    `NAME.md`. It also installs `script/install` and `script/update-policy` in
-    the repo, so a repo updated once can update itself. The list of vendored
-    files is at the top of `script/install`. The script replaces each file and
-    keeps only the repo's own entries:
+    `NAME.md`. It also writes `script/fetch-policy` and `script/update-policy`
+    into the repo, so a repo updated once can update itself. The list of
+    vendored files is at the top of `script/fetch-policy`. The script replaces
+    each file and keeps only the repo's own entries:
     - in `.gitignore`, `.editorconfig` and `.dockerignore`: the lines below the
       comment that ends the canonical file
     - in a `.gitignore` or `.dockerignore` lacking that comment: every entry the
@@ -1182,7 +1182,7 @@ style conventions are in separate documents:
     - `Makefile`
     - `script/` entrypoints (`bootstrap`, `setup`, `projectname`, `test`,
       `lint`, `fmt`, `fmt-check`, `check`, `docker`, `cibuild`, `precommit`,
-      `install-precommit`, `install`, `update-policy`)
+      `install-precommit`, `fetch-policy`, `update-policy`)
     - `Dockerfile`, `.dockerignore`
     - `.gitea/workflows/check.yml`
     - Go: `go.mod`, `go.sum`, `.golangci.yml`