UI: seven themes, each dark and light, chosen in the Settings

Settings > Theme and Settings > Light or dark pick the colours of every
screen (issue #10): roro9stack (the website's, the default), Catppuccin,
Dracula, Nord, ANSI terminal, Gruvbox and Solarized.

- A palette is 14 roles (lib/ui/src/palette.h). theme::kText and the
  others are now references into the one in use, so the Apps are
  unchanged; the main loop applies it when a Setting changes.
- Every colour is one the RGB332 frame buffer holds exactly: the themes'
  own were rounded, and those that fell together or lost contrast were
  picked by hand. test_palette checks exactness and 18 contrast ratios
  for each palette.
- The Sky view's constellation colours come from the theme.
- `theme [0-6] [light|dark]` on the consoles.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

src/ui/screen.h

@@ -14,6 +14,8 @@ class Screen {
     // Takes over the screen while a Firmware Update is received or about to restart.
     void renderUpdate(const std::string& title, const std::string& detail, int percent);
     Canvas& canvas() { return canvas_; }
+    // The colours changed: an App that keeps what it drew has to draw it all again.
+    void invalidate() { lost_ = true; }
 
    private:
     Canvas canvas_;

src/ui/theme.h

@@ -2,22 +2,31 @@
 
 #include <cstdint>
 
+#include "palette.h"
+
 namespace roro::theme {
 
-// The website's palette (site/static/css/site.css, its dark side), as RGB565. Every one is a colour
-// the 8-bit frame buffer (RGB332) holds exactly, so what is asked for is what is shown.
-constexpr uint16_t kBackground = 0x0000;
-constexpr uint16_t kText = 0xFFFF;
-constexpr uint16_t kAccent = 0x06DF;     // cyan, #00dbff: what is chosen, what is live
-constexpr uint16_t kOnAccent = 0x000A;   // dark blue, #000055: text and pictures on a cyan fill
-constexpr uint16_t kSelection = kAccent; // behind a selected row, whose text is kOnAccent
-constexpr uint16_t kMuted = 0x9495;      // grey, #9292aa: between the website's two
-constexpr uint16_t kFaint = 0x4A4A;      // slate, #494955: grid lines, what stays behind
-constexpr uint16_t kBar = kFaint;        // Status Bar background
-constexpr uint16_t kBarMuted = 0xB5B5;   // light grey, #b6b6aa: what is idle, on the bar
-constexpr uint16_t kWarning = 0xFC80;    // orange, #ff9200
-constexpr uint16_t kMessage = 0xFC9F;    // pink, #ff92ff: someone wrote
-constexpr uint16_t kGood = 0x4ECA;       // green, #49db55: a Fix, the best of a set (not on the website)
+// The colours every screen draws with: the theme chosen in the Settings (issue #10, lib/ui's
+// palette.h), set at boot and whenever it changes. They read as constants, and are references into
+// the palette in use, so a draw after apply() is in the new colours.
+inline ui::Palette current = ui::palette(0, false);
+inline void apply(const ui::Palette& p) { current = p; }
+
+inline const uint16_t& kBackground = current.background;
+inline const uint16_t& kText = current.text;
+inline const uint16_t& kAccent = current.accent;       // what is chosen, what is live
+inline const uint16_t& kOnAccent = current.onAccent;   // text and pictures on an accent fill
+inline const uint16_t& kSelection = current.accent;    // behind a selected row, whose text is kOnAccent
+inline const uint16_t& kMuted = current.muted;
+inline const uint16_t& kFaint = current.faint;         // grid lines, what stays behind
+inline const uint16_t& kBar = current.bar;             // Status Bar background
+inline const uint16_t& kBarMuted = current.barMuted;   // what is idle, on the bar
+inline const uint16_t& kWarning = current.warning;
+inline const uint16_t& kMessage = current.message;     // someone wrote
+inline const uint16_t& kGood = current.good;           // a Fix, the best of a set
+inline const uint16_t& kRed = current.red;             // these three: to tell things apart
+inline const uint16_t& kYellow = current.yellow;
+inline const uint16_t& kViolet = current.violet;
 
 constexpr int kWidth = 240;
 constexpr int kHeight = 135;