Fix centering adding vertical space and displacing the progress bar

render.Row(expanded=True, main_align="center") correctly centered the
time/temp text horizontally, but `expanded` also grabbed extra
*vertical* space from the enclosing Column (main_align="space_between"),
which pushed the progress bar further down than intended.

Replaced with a computed left Padding instead -- only nudges this one
line horizontally, so it can't affect the Column's vertical
distribution the way a flexible/expanding child can. tom-thumb is
variable-width, so the padding amount is an estimate (~3.9px/char,
measured via the CLI against several real time/temp strings) rather
than pixel-exact, but close enough not to look off-center for strings
in the length range this branch allows.

Separately verified (pixel-sampled, not just eyeballed) that the
progress bar was never actually missing -- confirmed present with the
exact "bar_empty" color at every recent commit, including before this
fix. It's just low-contrast at 0% progress (dark purple on near-black),
which is what a one-shot `pixlet render` always shows (empty cache ->
elapsed=0 -> fraction=0.0), not a regression.

subwave_nowplaying.star

@@ -245,8 +245,23 @@ def main(config):
     # scrolling it -- easy to mistake for "the centering didn't work").
     time_temp_char_count = len(list(now["time_temp"].codepoints()))
     time_temp_fits = scale == 2 and time_temp_char_count <= 15
+
+    # Centered via a computed left Padding, not render.Row(expanded=True,
+    # main_align="center") -- that version centered the text correctly,
+    # but Row's `expanded` also grabbed extra *vertical* space from the
+    # enclosing Column (main_align="space_between"), which pushed the
+    # progress bar below it out of view. Padding only nudges this one
+    # line horizontally, so it can't affect the Column's vertical
+    # distribution the way a flexible/expanding child can.
+    #
+    # tom-thumb is variable-width, so this is an estimate (~3.9px/char,
+    # measured via the CLI against several real time/temp strings), not
+    # pixel-exact centering -- close enough that it isn't visibly
+    # off-center for strings in the length range this branch allows.
+    estimated_text_width = int(time_temp_char_count * 3.9)
+    pad_left = max(0, (text_width - estimated_text_width) // 2)
     time_temp_line = (
-        render.Box(width = text_width, child = render.Row(main_align = "center", expanded = True, children = [time_temp_text]))
+        render.Padding(pad = (pad_left, 0, 0, 0), child = time_temp_text)
         if time_temp_fits else
         render.Marquee(width = text_width, child = time_temp_text)
     )