Dash: DIN 1451 opt-in per widget (hudFont), GNSS compass, rei by default; widget catalogue

From smart-serow: the DIN 1451 face (Alte DIN 1451 Mittelschrift, via gps-speedo)
and GpsCompass. A cosmetic font is opt-in: widgets name hudFont in their own
TextStyle, the rest keeps the basic font (CJK). Boxes and telltales shrink long
labels instead of wrapping. Telltale and Reading get their own files;
lib/README.md catalogues folders and widgets like smart-serow's.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

lib/README.md

@@ -0,0 +1,34 @@
+---
+type: reference
+---
+# The app's code: a catalogue
+
+Laid out like smart-serow's HUD (`pi/ui/lib/`), which several pieces come from.
+
+## Folders
+
+| Where | Holds |
+|---|---|
+| `lib/*.dart` | Pages (`dash`, `checklist`, `camview`, `linktest`), the boundary client (`boundary`), the USB network binding (`net`), and `reading`, one signal's state as a display needs it |
+| `theme/` | `palette.dart`: the palette and `hudFont` |
+| `widgets/` | Reusable display widgets, one per file, each fed values, never the boundary |
+
+## Widgets
+
+| Widget | File | Shows | From |
+|---|---|---|---|
+| `StatBox`, `StatBoxMain` | `widgets/stat_box.dart` | A value, its unit and label, sized from its box's height; highlight on warning, subdued when dim | smart-serow |
+| `Telltale` | `widgets/telltale.dart` | An on/off lamp: a label or an icon, lit or dark, "—" when missing | Yukart |
+| `WhiskeyMark` | `widgets/whiskey_mark.dart` | Attitude: a horizon tilting with roll, ladder moving with pitch | smart-serow |
+| `AccelGraph` | `widgets/accel_graph.dart` | G-meter: a dot for lateral/longitudinal g, a trace and a peak marker over a window | smart-serow |
+| `GpsCompass` | `widgets/gps_compass.dart` | Heading arrow and bearing; "ACQ" while acquiring, "N/A" without | smart-serow, from gps-speedo |
+
+## Conventions
+
+- **The boxed pattern.** A widget takes its share of a row and sizes its type from its own height, so a layout
+  is a grid of boxes and a value gaining a digit never moves anything. Labels shrink to fit, never wrap.
+- **Colours by meaning.** `AppTheme.of(context)` gives the palette's `background`, `foreground`, `highlight` and
+  `subdued`; no widget names a colour. Themes are smart-serow's JSON (`assets/themes/`), `rei` by default.
+- **Cosmetic fonts are opt-in.** A widget that wants the HUD face names `fontFamily: hudFont` in its own
+  `TextStyle`; everything else keeps the basic font, which covers CJK where DIN 1451 does not.
+- **Missing is a state** (app guideline 2): a widget given no value draws "—" or subdued, never an error.