Add CalVer versioning and rebuild the song page's fact line

Versions are YYYY.MM.DD-N, injected with -ldflags from a git tag, so no file
in the repo carries the number and a local build honestly says dev. The
version shows in the footer, the startup log and /healthz.

The song page's metadata was five different kinds of fact — artist, genre,
duration, provenance and a badge about the viewer — in one flat run with two
competing pills. Now the artist has its own line in the display face, and the
facts sit in four labelled cells like the spine of a cassette insert. The
submitter links to their profile, "oma kappale" became "lähetti: sinä", and
the clock time is gone: nobody needs the minute a song was published.

render.go

@@ -16,8 +16,10 @@ var assetFS embed.FS
 
 var funcs = template.FuncMap{
 	"fidate": func(t time.Time) string { return t.Local().Format("2.1.2006 15:04") },
-	"score":  func(f *float64) string { return strconv.FormatFloat(*f, 'f', 1, 64) },
-	"value":  func(f float64) string { return strconv.FormatFloat(f, 'f', 1, 64) },
+	// Date without the clock: the minute a song was published is noise.
+	"fiday": func(t time.Time) string { return t.Local().Format("2.1.2006") },
+	"score": func(f *float64) string { return strconv.FormatFloat(*f, 'f', 1, 64) },
+	"value": func(f float64) string { return strconv.FormatFloat(f, 'f', 1, 64) },
 	// Lets one board partial be called with a title and a list, instead of two near-identical
 	// partials per leaderboard.
 	"dict": func(pairs ...any) map[string]any {
@@ -51,14 +53,15 @@ func init() {
 
 // page is everything the layout needs, plus whatever the page itself wants in Data.
 type page struct {
-	Title  string
-	Member *member
-	Admin  bool
-	Flash  string
-	Path   string
-	Narrow bool // auth pages are a 420px column
-	Queued int  // songs still owed a review, shown in the nav
-	Data   any
+	Title   string
+	Member  *member
+	Admin   bool
+	Flash   string
+	Path    string
+	Narrow  bool // auth pages are a 420px column
+	Queued  int  // songs still owed a review, shown in the nav
+	Version string
+	Data    any
 }
 
 func (a *app) render(w http.ResponseWriter, r *http.Request, status int, name string, p page) {
@@ -70,6 +73,7 @@ func (a *app) render(w http.ResponseWriter, r *http.Request, status int, name st
 	}
 	p.Member = memberFrom(r.Context())
 	p.Path = r.URL.Path
+	p.Version = version
 	if p.Member != nil {
 		// The queue is a worklist, so its size belongs in the nav.
 		a.pool.QueryRow(r.Context(), `