feat(player): show progress on the phone's bar border

#59 took the seek bar off the phone's transport, so the one thing a
mini player is expected to say without being opened -- how far through
the song it is -- had nowhere left to be said.

It is the shell's element and its own 2px grid row between `bottom-bar`
and `bottom-nav`, because those two are separate components and either
one drawing the line means reaching into the other's box. The fill is
`scaleX()` off the same `PlaybackPositionChanged` the seek bar renders,
with the same `trackChangeId`/`seq` guards and an interval that only
interpolates *between* reports -- never its own clock, which is the
rule that exists because a local counter drifted 30 s away from the
backend across four keyboard seeks.

It is `aria-hidden` and takes no pointer events at any depth: Now
Playing's seek bar is what announces the position, and a 2px strip on
the top edge of the tab bar is exactly where a thumb aiming at a tab
lands. It renders nothing above 600px, from `matchMedia` rather than a
media query, because a stylesheet cannot stop a 1 Hz interval running
for the life of every desktop session about a line nobody can see.

Its phone rule is at the foot of index.css beside `job-band`'s, not in
the phone block above: a media query adds no specificity, so a
`display: block` written before the `display: none` that takes it out
of the desktop grid loses to it and the line never appears at all.

Closes #58

CLAUDE.md

@@ -1909,6 +1909,33 @@ every desktop button from 33×21 to 36×24, silently. The sizes are
 asserted as `'33x21'` rather than as a range, because the regression
 was three pixels.
 
+**What that bar lost is how far through the song it is, and
+`<player-progress-line>` is where it went** (#58). #59 took the seek
+bar off the phone's transport, so the one thing a mini player is
+expected to say without being opened had nowhere left to be said. It is
+a 2px line on the border between the mini player and the tab bar: the
+**shell's** element and its own `auto` grid row between `bottom-bar`
+and `bottom-nav`, because those two are separate components and either
+one drawing it means reaching into the other's box for two pixels.
+
+Four things about it are load-bearing. **It never counts** — the fill is
+`scaleX()` off the same `PlaybackPositionChanged` the seek bar renders,
+with the same `trackChangeId` and `seq` guards and an interval that is
+stopped and restarted by every report, which is the rule that exists
+because a local clock drifted 30 s away across four keyboard seeks.
+**It is not a control and cannot become one**: `aria-hidden` on the host
+and `pointer-events: none` throughout, because Now Playing's seek bar
+is what announces the position and a 2px strip on the top edge of the
+tab bar is exactly where a thumb aiming at a tab lands. **It renders
+nothing above 600px**, from `matchMedia` rather than a media query, for
+`job-band`'s reason plus one of its own — a stylesheet cannot stop a
+1 Hz interval running for the life of every desktop session about a
+line nobody can see. And **its phone rule sits at the foot of
+`index.css`, beside `job-band`'s**, not in the phone block above: a
+media query adds no specificity, so a `display: block` written before
+the `display: none` that takes it out of the desktop grid loses to it
+and the line never appears at any width, silently.
+
 **900 is the worst desktop width, not the 800×600 minimum.** The
 sidebar collapses to icons *below* 900, so the main panel is 843px at
 899 and 700px at 900 — the narrowest content area any desktop width