Build 19: open-wallet shortcuts, Pay QR scan, configurable pairing, hide yellow

- Lower-left sidebar cards are now individual shortcuts: tapping the
  identity chip opens identity settings, tapping the node card jumps
  straight to the Node menu (was: both opened generic settings).
- Pay screen gains a scan-to-pay QR puck top-right that opens the camera
  and prefills the recipient while keeping the typed amount (reuses the
  Home scan + SendFlow::request_scan/prefill_amount path).
- Replace the USD-only "fiat preview" with a configurable "Pairing":
  Off / USD / EUR / GBP / JPY / CNY / Bitcoin / Sats (default USD). price.rs
  now fetches GRIN against any vs_currency (sats price vs btc, ×1e8) and
  caches per code; a Settings → Pairing sub-page picks it; the Pay, send,
  and balance previews all route through one pairing_preview() helper.
- Hide the Yellow theme from the picker (cycle is Dark ↔ Light now); the
  ThemeKind::Yellow tokens stay defined — it's beta, not removed.

Verified live on :2 (Default wallet): node card → Node menu; identity chip
→ identity settings; QR puck renders top-right of Pay; Pairing → Sats shows
"≈ 1,912 sats" for 50ツ over a live BTC rate, resets to USD; theme cycles
Dark↔Light, never Yellow. 34 lib tests green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/settings/config.rs

@@ -75,8 +75,10 @@ pub struct AppConfig {
 	density: Option<String>,
 	/// Identifier of the last opened wallet to boot into.
 	last_wallet_id: Option<i64>,
-	/// Show fiat (USD) preview alongside amounts.
+	/// Show fiat (USD) preview alongside amounts (legacy; migrated to pairing).
 	fiat_preview: Option<bool>,
+	/// Amount pairing code: off|usd|eur|gbp|jpy|cny|btc|sats (default usd).
+	pairing: Option<String>,
 
 	/// Flag to use proxy for network requests.
 	use_proxy: Option<bool>,
@@ -93,6 +95,85 @@ pub struct AppConfig {
 	app_update: Option<AppUpdate>,
 }
 
+/// What the amount preview is paired to: nothing, a fiat currency, or bitcoin.
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum Pairing {
+	Off,
+	Usd,
+	Eur,
+	Gbp,
+	Jpy,
+	Cny,
+	Btc,
+	Sats,
+}
+
+impl Pairing {
+	/// All variants, in picker order.
+	pub const ALL: [Pairing; 8] = [
+		Pairing::Off,
+		Pairing::Usd,
+		Pairing::Eur,
+		Pairing::Gbp,
+		Pairing::Jpy,
+		Pairing::Cny,
+		Pairing::Btc,
+		Pairing::Sats,
+	];
+
+	/// Stable config code.
+	pub fn code(&self) -> &'static str {
+		match self {
+			Pairing::Off => "off",
+			Pairing::Usd => "usd",
+			Pairing::Eur => "eur",
+			Pairing::Gbp => "gbp",
+			Pairing::Jpy => "jpy",
+			Pairing::Cny => "cny",
+			Pairing::Btc => "btc",
+			Pairing::Sats => "sats",
+		}
+	}
+
+	pub fn from_code(s: &str) -> Option<Pairing> {
+		Some(match s {
+			"off" => Pairing::Off,
+			"usd" => Pairing::Usd,
+			"eur" => Pairing::Eur,
+			"gbp" => Pairing::Gbp,
+			"jpy" => Pairing::Jpy,
+			"cny" => Pairing::Cny,
+			"btc" => Pairing::Btc,
+			"sats" => Pairing::Sats,
+			_ => return None,
+		})
+	}
+
+	/// The CoinGecko `vs_currency` to price against (sats prices vs btc).
+	/// `None` when pairing is off.
+	pub fn vs_currency(&self) -> Option<&'static str> {
+		match self {
+			Pairing::Off => None,
+			Pairing::Sats => Some("btc"),
+			other => Some(other.code()),
+		}
+	}
+
+	/// Human label for the picker / settings row.
+	pub fn label(&self) -> &'static str {
+		match self {
+			Pairing::Off => "Off",
+			Pairing::Usd => "USD",
+			Pairing::Eur => "EUR",
+			Pairing::Gbp => "GBP",
+			Pairing::Jpy => "JPY",
+			Pairing::Cny => "CNY",
+			Pairing::Btc => "Bitcoin",
+			Pairing::Sats => "Sats",
+		}
+	}
+}
+
 impl Default for AppConfig {
 	fn default() -> Self {
 		Self {
@@ -112,6 +193,7 @@ impl Default for AppConfig {
 			density: None,
 			last_wallet_id: None,
 			fiat_preview: None,
+			pairing: None,
 			use_proxy: None,
 			use_socks_proxy: None,
 			http_proxy_url: None,
@@ -363,17 +445,25 @@ impl AppConfig {
 		w_config.save();
 	}
 
-	/// Check if fiat (USD) preview is enabled (default on).
-	pub fn fiat_preview() -> bool {
+	/// What amount previews are paired to (default USD). Migrates the legacy
+	/// `fiat_preview = false` to `Off`.
+	pub fn pairing() -> Pairing {
 		let r_config = Settings::app_config_to_read();
-		r_config.fiat_preview.unwrap_or(true)
+		if let Some(code) = r_config.pairing.clone() {
+			if let Some(p) = Pairing::from_code(&code) {
+				return p;
+			}
+		}
+		match r_config.fiat_preview {
+			Some(false) => Pairing::Off,
+			_ => Pairing::Usd,
+		}
 	}
 
-	/// Toggle fiat preview.
-	pub fn toggle_fiat_preview() {
-		let enabled = Self::fiat_preview();
+	/// Save the amount pairing.
+	pub fn set_pairing(p: Pairing) {
 		let mut w_config = Settings::app_config_to_update();
-		w_config.fiat_preview = Some(!enabled);
+		w_config.pairing = Some(p.code().to_string());
 		w_config.save();
 	}