feat: stats timeline, band-map colours, frameless window, and four fixes

Statistics — the activity chart ignored the period selector: picking a year up
top left it showing the last 7 days, two controls contradicting each other. The
buttons were four fixed rolling windows anchored on the newest QSO, not
granularities. They now choose the BUCKET SIZE over the selected period, with an
Auto default and a step-up when a bucket would be too fine (the backend drops a
series past 750 buckets rather than ship 6000 unreadable bars). The hour-of-day
histogram covered a single day, too little to read anything from; it moves to
its own card with a weekday view, over the whole period.

Band map — the CW/data/phone sub-bands were shaded with the STATUS tokens, the
same amber that means "new band" on the pills drawn on top of them. A sub-band
is an identity, not a state: categorical hues now, validated in both themes
(violet failed on the dark steps — 1.9 ΔE from blue for a protan reader) and
added to the legend, since identity must never be colour-alone.

Frameless window — the OS title bar was a dead 32px band above a window that
already has its own. Minimise/maximise/close move into the app header, which
carries the drag region and double-click-to-maximise. The drag opt-out is by
ROLE in CSS, so a future button in that bar keeps working without anyone
remembering the rule.

Fixes:
- Saving settings froze the window while a device was slow: restarting a link
  waits for its poll goroutine, which can sit 45 s inside an uninterruptible COM
  Connect when another program holds the rig. The restart is now off the UI
  path; a slow one is logged.
- Multi-screen: a MAXIMISED window was never repositioned, so it came back on
  the primary screen every launch. The corner is now recorded even when
  maximised (it names the monitor) and re-applied while still hidden.
- The Callsign field is marked out at rest — operators were typing the call into
  Name, which sat beside it and looked identical.
- QSL dates get a real picker (native, for the OS calendar and locale order); a
  malformed old value stays in a text box rather than vanishing behind an empty
  one.

Also: a Support OpsLog entry in Help, and a WinKeyer protocol trace. The WK2
report (one element then a ten-second pause, sidetone that will not switch off)
is NOT fixed here: the WK1/WK2/WK3 command sets differ and a guessed fix would
break the operators it works for today. The trace logs every byte with the
command name and spells out the firmware family, which is what will settle it.

frontend/src/style.css

@@ -652,3 +652,37 @@
   border: 2px solid var(--background);
 }
 ::-webkit-scrollbar-thumb:hover { background: var(--scrollbar-thumb-hover); }
+
+/* ── Frameless window: drag region ──────────────────────────────────────────
+   The OS title bar is gone (main.go, Frameless), so the app header IS the title
+   bar and must be draggable. Everything interactive inside it opts OUT: a drag
+   region swallows clicks, and without this the menus and toolbar buttons would
+   move the window instead of doing their job. Opting out by ROLE rather than
+   listing each child keeps a future button working without anyone remembering
+   this rule. */
+.app-dragregion {
+  --wails-draggable: drag;
+}
+.app-dragregion button,
+.app-dragregion a,
+.app-dragregion input,
+.app-dragregion select,
+.app-dragregion textarea,
+.app-dragregion nav,
+.app-dragregion [role='button'],
+.app-dragregion [role='menu'],
+.app-dragregion [data-no-drag] {
+  --wails-draggable: no-drag;
+}
+
+/* Native date inputs: the WebView draws its calendar glyph in near-black, which
+   disappears on the dark themes. Invert it there — the control itself is worth
+   keeping (OS calendar, locale date order, keyboard entry), only its icon needs
+   help. */
+[data-theme='dim-slate'] input[type='date']::-webkit-calendar-picker-indicator,
+[data-theme='dark-warm'] input[type='date']::-webkit-calendar-picker-indicator,
+[data-theme='dark-graphite'] input[type='date']::-webkit-calendar-picker-indicator,
+[data-theme='high-contrast'] input[type='date']::-webkit-calendar-picker-indicator {
+  filter: invert(1) brightness(1.6);
+  opacity: 0.75;
+}