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>

internal/client/client.go

@@ -183,7 +183,7 @@ func (c *Client) Do(ctx context.Context, method, path string, query url.Values,
 		req.Header.Set("Content-Type", "application/json")
 	}
 	req.Header.Set("Accept", "application/json")
-	req.Header.Set("User-Agent", "jarl-cli/"+version.Version)
+	req.Header.Set("User-Agent", "jarl-cli/"+version.Short())
 	if c.Token != "" {
 		req.Header.Set("Authorization", "Bearer "+c.Token)
 	}