Fall back to dev when git describe prints nothing (closes #74)

The Makefile example in the Go styleguide and in the HTTP server conventions
set VERSION from `git describe --tags --always` alone. Outside a git checkout,
such as an unpacked source tarball, that prints nothing, so the binary was
stamped with an empty version and nothing said so. Both now read
`VERSION ?= $(or $(shell git describe --tags --always 2>/dev/null),dev)`, and
the comment above each says so. A `VERSION` from the environment or the make
command line still takes precedence.

Model: opus-5-5

TODO.md

@@ -21,6 +21,11 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-04: The Makefile examples in the Go styleguide and the HTTP server
+  conventions now fall back to `dev` when `git describe` prints nothing, as it
+  does outside a git checkout, instead of stamping an empty version (issue 74).
+  The canonical `Dockerfile` already fails on a `dev` version when `.git` is in
+  the build context.
 - 2026-10-03: Moved the canonical golangci-lint to v2.14.0, built with go1.27,
   because v2.12.2 refuses to lint a module whose `go` directive is 1.27 (issue
   65). Releases from v2.13.0 deprecate `exhaustruct` in favour of