feat(ui): keyboard overhaul — shared instance, icon keys, symbols page

- Unify on the shared keyboard: WaypointsView drives UITask::keyboard()
  instead of its own instance; openKb() clears {loc}/{time} for literal
  fields (labels, coordinates). Reclaims the duplicate widget from the heap.
- Icon glyphs on the special row: caps ⇧, space ⎵ (two halves), delete ⌫,
  OK ✓ (reuses ICON_CHECK); {} and the page toggle stay text.
- Second character page (symbols), toggled by a "#@"/"abc" key. Tidy the
  letters page: drop the duplicate grid space, add the comma, group
  punctuation as . , ! ?
- Harden the preview buffers (KB_PREVIEW_CAP) against very wide displays.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/icons.h

@@ -87,6 +87,36 @@ MINI_ICON(ICON_CROSS, 4,   // ✗
   packRow(".##."),
   packRow("#..#"));
 
+// Keyboard special-key glyphs.
+MINI_ICON(ICON_SHIFT, 7,   // ⇧  caps
+  packRow("...#..."),
+  packRow("..###.."),
+  packRow(".#####."),
+  packRow("#######"),
+  packRow("..###.."),
+  packRow("..###.."),
+  packRow("..###.."));
+MINI_ICON(ICON_BACKSPACE, 8,   // ⌫  delete-left (× knocked out of the arrow body)
+  packRow("...#####"),
+  packRow("..######"),
+  packRow(".###.#.#"),
+  packRow("#####.##"),
+  packRow(".###.#.#"),
+  packRow("..######"),
+  packRow("...#####"));
+// Space ⎵ is wider than the 8-px mini-icon limit, so it is two halves drawn
+// side by side (offset by ICON_SPACE_L.w * scale): ticks at both far ends + bar.
+MINI_ICON(ICON_SPACE_L, 8,
+  packRow("#......."),
+  packRow("#......."),
+  packRow("#......."),
+  packRow("########"));
+MINI_ICON(ICON_SPACE_R, 8,
+  packRow(".......#"),
+  packRow(".......#"),
+  packRow(".......#"),
+  packRow("########"));
+
 // ── Big ASCII-art icons (skeleton, not yet used) ─────────────────────────────
 // Same authoring idea as the mini-icons but for full page glyphs up to 32 px
 // wide: one uint32_t per row. The existing XBM bitmaps below (logo/bluetooth/…)