Run golangci-lint only in docker, on every run (closes #55)

script/lint builds the new Dockerfile.lint, where golangci-lint runs as
a build step. The lint stage is rebuilt on every run, so an unchanged
tree is linted too; the module download stays cached. script/bootstrap
no longer installs golangci-lint. The Dockerfile lint stage calls
golangci-lint directly, since make lint now starts a docker build.
golangci-lint config verify is not run: it fetches its schema live over
unpinned HTTPS.

Model: opus-5-5

TODO.md

@@ -25,6 +25,13 @@ Bring the repo into policy compliance in one commit:
 
 # Completed Steps
 
+- 2026-10-04: Lint runs only in docker: `script/lint` builds
+  `Dockerfile.lint`, where golangci-lint is a build step rebuilt on
+  every run (`--no-cache-filter`), so an unchanged tree is linted too;
+  the module download stays cached. `script/bootstrap` no longer
+  installs golangci-lint, and the `Dockerfile` lint stage calls it
+  directly instead of `make lint`. `golangci-lint config verify` is not
+  run: it fetches its schema live over unpinned HTTPS.
 - 2026-10-03: `secret mv` rejects a move whose destination is the
   source (`mv --force x x`, `mv --force work:x work:`, or an empty
   destination, which defaults to the source name) before changing