feat: show dev-<sha> version string in nav for dev builds

Production images continue to display the semver (v1.x.x). Dev images
built by CI now receive BUILD_VERSION=dev-<7-char-sha> via a Docker ARG,
and app.js skips the v prefix for non-semver strings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/helpers.test.js

@@ -115,6 +115,24 @@ describe('fmtDateFull', () => {
   })
 })
 
+// ── versionLabel() ───────────────────────────────────────────────────────────
+// Mirrors the logic in app.js — semver strings get a v prefix, dev strings don't.
+
+function versionLabel(v) {
+  return /^\d/.test(v) ? `v${v}` : v
+}
+
+describe('version label formatting', () => {
+  it('prepends v for semver strings', () => {
+    expect(versionLabel('1.1.2')).toBe('v1.1.2')
+    expect(versionLabel('2.0.0')).toBe('v2.0.0')
+  })
+
+  it('does not prepend v for dev build strings', () => {
+    expect(versionLabel('dev-abc1234')).toBe('dev-abc1234')
+  })
+})
+
 // ── CSS regressions ───────────────────────────────────────────────────────────
 
 const css = readFileSync(join(__dirname, '../css/app.css'), 'utf8')
@@ -127,3 +145,15 @@ describe('CSS regressions', () => {
     expect(css).toMatch(/\.badge\s*\{[^}]*text-align\s*:\s*center/s)
   })
 })
+
+// ── CI workflow regressions ───────────────────────────────────────────────────
+
+const ciYml = readFileSync(join(__dirname, '../.gitea/workflows/ci.yml'), 'utf8')
+
+describe('CI workflow regressions', () => {
+  it('build-dev job passes BUILD_VERSION build arg', () => {
+    // Regression: dev image showed semver instead of dev-<sha> because
+    // BUILD_VERSION was never passed to docker build.
+    expect(ciYml).toContain('BUILD_VERSION')
+  })
+})