Run the linter only in Docker (closes #20)

script/lint now builds only the lint stage of the Dockerfile, without
the build cache, so every run executes the linter; the image is tagged
simplelog-lint. The lint stage calls golangci-lint directly, since make
lint is itself a docker build of that stage. script/cibuild and
script/docker also build without the cache, so their check steps always
run. script/fmt no longer runs golangci-lint --fix, and script/bootstrap
no longer installs it. golangci-lint config verify is left out, on the
owner's ruling. The README, TODO.md and the script/cibuild comment say
what now runs.

Model: opus-5-5

README.md

@@ -131,8 +131,9 @@ alpine. We provide:
   extension)
 - `script/docker` — build the Docker image without the build cache, tagged
   via `script/projectname` (byte-identical across repos)
-- `script/cibuild` — cd to the repo root and `docker build --no-cache .` (what
-  CI runs; the image build runs the checks)
+- `script/cibuild` — cd to the repo root and build the Docker image without the
+  build cache, tagged via `script/projectname` (what CI runs; the image build
+  runs the checks)
 - `script/precommit` — run by the git pre-commit hook (our own extension);
   runs a `go mod tidy` guard, then `script/check`
 - `script/install-precommit` — installs the git pre-commit hook (our own

script/cibuild

@@ -4,11 +4,12 @@
 # --no-cache because a cached check step is a check that did not run.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    docker build --no-cache .
+    docker build --no-cache -t "$("$SCRIPT_DIR/projectname")" .
 }
 
 main "$@"