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/embedded-storage/src/iter.rs

@@ -0,0 +1,64 @@
+use crate::Region;
+
+/// Iterator producing block-region pairs, where each memory block maps to each
+/// region.
+pub struct OverlapIterator<'a, R, I>
+where
+	R: Region,
+	I: Iterator<Item = R>,
+{
+	memory: &'a [u8],
+	regions: I,
+	base_address: u32,
+}
+
+/// Trait allowing us to automatically add an `overlaps` function to all iterators over [`Region`]
+pub trait IterableByOverlaps<'a, R, I>
+where
+	R: Region,
+	I: Iterator<Item = R>,
+{
+	/// Obtain an [`OverlapIterator`] over a subslice of `memory` that overlaps with the region in `self`
+	fn overlaps(self, memory: &'a [u8], base_address: u32) -> OverlapIterator<R, I>;
+}
+
+impl<'a, R, I> Iterator for OverlapIterator<'a, R, I>
+where
+	R: Region,
+	I: Iterator<Item = R>,
+{
+	type Item = (&'a [u8], R, u32);
+
+	fn next(&mut self) -> Option<Self::Item> {
+		while let Some(region) = self.regions.next() {
+			//  TODO: This might be possible to do in a smarter way?
+			let mut block_range = (0..self.memory.len())
+				.skip_while(|index| !region.contains(self.base_address + *index as u32))
+				.take_while(|index| region.contains(self.base_address + *index as u32));
+			if let Some(start) = block_range.next() {
+				let end = block_range.last().unwrap_or(start) + 1;
+				return Some((
+					&self.memory[start..end],
+					region,
+					self.base_address + start as u32,
+				));
+			}
+		}
+		None
+	}
+}
+
+/// Blanket implementation for all types implementing [`Iterator`] over [`Regions`]
+impl<'a, R, I> IterableByOverlaps<'a, R, I> for I
+where
+	R: Region,
+	I: Iterator<Item = R>,
+{
+	fn overlaps(self, memory: &'a [u8], base_address: u32) -> OverlapIterator<R, I> {
+		OverlapIterator {
+			memory,
+			regions: self,
+			base_address,
+		}
+	}
+}