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. Where that prints
nothing (outside a git checkout, or where git is missing or refuses the
checkout), 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 names that condition. 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 (outside
+  a git checkout, or where git is missing or refuses the 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.
 - 2026-10-04: The canonical `.dockerignore` now also keeps out each submodule's
   `config` (issue 75). A submodule's git directory lives under `.git/modules/`,
   nested again for its own submodules, and its `config` can hold a credential