Stamp the git commit into images built from the Dockerfile (closes #236)

.dockerignore left out .git, so `make build` in the image found no git
metadata and stamped `dev`. It now sends .git, and no longer leaves out
tracked files (LICENSE, README.md, ...), which git would see as deleted
and mark the version -dirty. The footer and /health already read the
same version. The startup log line that reports it, the logger's
Identify(), was never called; main now calls it. The README says to
build from a git clone.

Model: opus-5-5

TODO.md

@@ -20,6 +20,12 @@ regress.
 
 # Completed Steps
 
+- 2026-09-29: An image built from the `Dockerfile` now shows the commit it was
+  built from (the `git describe` output) in the footer and `/health` instead of
+  `dev`: `.dockerignore` no longer leaves out `.git`, nor any tracked file,
+  which git would count as deleted and mark `-dirty`. upaas now also logs its
+  version at startup; the logger's `Identify()` was never called (#236).
+
 - 2026-09-29: The app page shows the app's branch as a label in its title, next
   to the status badge, instead of after the repository under it (#240).