feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/micromath/src/float/log10.rs

@@ -0,0 +1,78 @@
+//! log base 2 approximation for a single-precision float.
+
+use super::F32;
+use core::f32::consts::LOG10_E;
+
+impl F32 {
+    /// Approximates the base 10 logarithm of the number.
+    pub fn log10(self) -> Self {
+        self.ln() * LOG10_E
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::F32;
+    pub(crate) const MAX_ERROR: f32 = 0.001;
+
+    /// log10(x) test vectors - `(input, output)`
+    pub(crate) const TEST_VECTORS: &[(f32, f32)] = &[
+        (1e-20, -20.0),
+        (1e-19, -19.0),
+        (1e-18, -18.0),
+        (1e-17, -17.0),
+        (1e-16, -16.0),
+        (1e-15, -15.0),
+        (1e-14, -14.0),
+        (1e-13, -13.0),
+        (1e-12, -12.0),
+        (1e-11, -11.0),
+        (1e-10, -10.0),
+        (1e-09, -9.0),
+        (1e-08, -8.0),
+        (1e-07, -7.0),
+        (1e-06, -6.0),
+        (1e-05, -5.0),
+        (1e-04, -4.0),
+        (0.001, -3.0),
+        (0.01, -2.0),
+        (0.1, -1.0),
+        (10.0, 1.0),
+        (100.0, 2.0),
+        (1000.0, 3.0),
+        (10000.0, 4.0),
+        (100000.0, 5.0),
+        (1000000.0, 6.0),
+        (10000000.0, 7.0),
+        (100000000.0, 8.0),
+        (1000000000.0, 9.0),
+        (10000000000.0, 10.0),
+        (100000000000.0, 11.0),
+        (1000000000000.0, 12.0),
+        (10000000000000.0, 13.0),
+        (100000000000000.0, 14.0),
+        (1000000000000000.0, 15.0),
+        (1e+16, 16.0),
+        (1e+17, 17.0),
+        (1e+18, 18.0),
+        (1e+19, 19.0),
+    ];
+
+    #[test]
+    fn sanity_check() {
+        assert_eq!(F32::ONE.log10(), F32::ZERO);
+
+        for &(x, expected) in TEST_VECTORS {
+            let ln_x = F32(x).log10();
+            let relative_error = (ln_x - expected).abs() / expected;
+
+            assert!(
+                relative_error <= MAX_ERROR,
+                "relative_error {} too large: {} vs {}",
+                relative_error,
+                ln_x,
+                expected
+            );
+        }
+    }
+}