Add author/homepage/license to version + banner; date format fixes

- globals.go: add Homepage and License constants.
- version command: show author, homepage, license, build date.
- Startup banner reformatted to:
    vaultik X by Author (commit Y, built on Z) starting up at T.
    https://sneak.berlin/go/vaultik
- Commit date now formatted as YYYY-MM-DD (called "build date" in
  user-facing output, since the binary was at least compiled once on
  the date of commit). Makefile/Dockerfile use git --format=%cs.
  goreleaser slices its RFC3339 .CommitDate template var to 10 chars.

internal/cli/app.go

@@ -46,9 +46,11 @@ func setupGlobals(lc fx.Lifecycle, g *globals.Globals, v *vaultik.Vaultik, opts
 				// user-facing output is suppressed.
 				v.UI = ui.NewWithColor(io.Discard, false)
 			} else {
-				v.UI.Banner("%s %s (commit %s, %s) invoked at %s by %s",
-					g.Appname, g.Version, g.ShortCommit(), g.CommitDate,
-					g.StartTime.Format(time.RFC3339), globals.Author)
+				v.UI.Banner("%s %s by %s (commit %s, built on %s) starting up at %s.",
+					g.Appname, g.Version, globals.Author,
+					g.ShortCommit(), g.CommitDate,
+					g.StartTime.Format(time.RFC3339))
+				v.UI.Banner("%s", globals.Homepage)
 			}
 			return nil
 		},