Report development builds as such, not as the release version

Only a release build (the commit tagged v<VERSION>, unchanged) gives a
version number. Others print 'dev <commit> (3 commits after v0.2.0-rc.1)',
from git describe (the Makefile's DESCRIBE), in jarld version,
jarl --version, jarl status, jarl whoami and the startup log; a build
without git says '(source build)'. The CLI's User-Agent and the footer's
tooltip follow suit, and /status's build gains since and ahead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -88,9 +88,13 @@ All notable changes to Jarl are documented here. The format follows
   linking to the release on Gitea. A build that isn't of a release tag
   shows its commit instead, linked to the commit and marked `-modified`
   with uncommitted changes. Before, every build of a commit after a
-  release still showed the release's version. `jarld version`,
-  `jarl --version`, `GET /status` and `/auth/whoami` report the same, the
-  latter two as `build` (docs/development.md).
+  release still showed the release's version. `GET /status` and
+  `/auth/whoami` report the build as `build` (docs/development.md).
+- `jarld version`, `jarl --version`, `jarl status` and `jarl whoami` give
+  a version number only for release builds. Other builds say they are
+  development builds and how far past the last tag they are: `dev
+  ca0f148b78b6 (3 commits after v0.2.0-rc.1)`. In 0.2.0-rc.1 they still
+  printed `0.2.0-rc.1 (ca0f148b78b6)`.
 - The view in the zone list, and on the zone page, links to that view,
   and the views page highlights it. It used to be plain text, and the zone
   page linked to the views page as a whole.