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/bitfield/examples/bits_position.rs

@@ -0,0 +1,75 @@
+#[macro_use]
+extern crate bitfield;
+
+use bitfield::BitMut;
+use bitfield::BitRangeMut;
+
+bitfield! {
+    struct BitsLocations([u8]);
+}
+
+bitfield! {
+    struct BitsLocationsMsb0(MSB0 [u8]);
+}
+
+fn println_slice_bits(slice: &[u8]) {
+    if slice.is_empty() {
+        println!("[]");
+    } else {
+        print!("[{:08b}", slice[0]);
+
+        for byte in &slice[1..] {
+            print!(", {:08b}", byte);
+        }
+
+        println!("]");
+    }
+}
+
+fn main() {
+    let mut bits_locations = BitsLocations([0; 3]);
+    let mut bits_locations_msb0 = BitsLocationsMsb0([0; 3]);
+
+    println!("Default version:");
+    for i in 0..(3 * 8) {
+        bits_locations.set_bit(i, true);
+        print!("{:2}: ", i);
+        println_slice_bits(&bits_locations.0);
+        bits_locations.set_bit(i, false);
+    }
+
+    for i in 0..(3 * 8 - 3) {
+        let msb = i + 3;
+        let lsb = i;
+        for value in &[0b1111u8, 0b0001, 0b1000] {
+            bits_locations.set_bit_range(msb, lsb, *value);
+            print!("{:2} - {:2} ({:04b}): ", msb, lsb, value);
+            println_slice_bits(&bits_locations.0);
+        }
+        println!();
+        bits_locations.set_bit_range(msb, lsb, 0u8);
+    }
+
+    println!("MSB0 version:");
+
+    for i in 0..(3 * 8) {
+        bits_locations_msb0.set_bit(i, true);
+        print!("{:2}: ", i);
+        println_slice_bits(&bits_locations_msb0.0);
+
+        bits_locations_msb0.set_bit(i, false);
+    }
+
+    for i in 0..(3 * 8 - 3) {
+        let msb = i + 3;
+        let lsb = i;
+        for value in &[0b1111u8, 0b0001, 0b1000] {
+            bits_locations_msb0.set_bit_range(msb, lsb, *value);
+            print!("{:2} - {:2} ({:04b}): ", msb, lsb, value);
+            println_slice_bits(&bits_locations_msb0.0);
+        }
+        println!();
+
+        bits_locations_msb0.set_bit_range(msb, lsb, 0u8);
+    }
+}

vendor/bitfield/examples/ipv4.rs

@@ -0,0 +1,60 @@
+#![allow(dead_code)]
+
+#[macro_use]
+extern crate bitfield;
+
+use std::net::Ipv4Addr;
+
+bitfield! {
+    struct IpV4Header(MSB0 [u8]);
+    impl Debug;
+    u32;
+    get_version, _: 3, 0;
+    get_ihl, _: 7, 4;
+    get_dscp, _: 13, 8;
+    get_ecn, _: 15, 14;
+    get_total_length, _: 31, 16;
+    get_identification, _: 47, 32;
+    get_df, _: 49;
+    get_mf, _: 50;
+    get_fragment_offset, _: 63, 51;
+    get_time_to_live, _: 71, 64;
+    get_protocol, _: 79, 72;
+    get_header_checksum, _: 95, 80;
+    u8, get_source_address, _: 103, 96, 4;
+    u32, into Ipv4Addr, get_destination_address, _: 159, 128;
+}
+
+impl<T: AsRef<[u8]>> IpV4Header<T> {
+    fn get_source_as_ip_addr(&self) -> Ipv4Addr {
+        let mut src = [0; 4];
+        for (i, src) in src.iter_mut().enumerate() {
+            *src = self.get_source_address(i);
+        }
+        src.into()
+    }
+}
+
+fn main() {
+    let data = [
+        0x45, 0x00, 0x00, 0x40, 0x69, 0x27, 0x40, 0x00, 0x40, 0x11, 0x4d, 0x0d, 0xc0, 0xa8, 0x01,
+        0x2a, 0xc0, 0xa8, 0x01, 0xfe,
+    ];
+
+    let header = IpV4Header(data);
+
+    assert_eq!(header.get_version(), 4);
+    assert_eq!(header.get_total_length(), 64);
+    assert_eq!(header.get_identification(), 0x6927);
+    assert!(header.get_df());
+    assert!(!header.get_mf());
+    assert_eq!(header.get_fragment_offset(), 0);
+    assert_eq!(header.get_protocol(), 0x11);
+    println!(
+        "from {} to {}",
+        header.get_source_as_ip_addr(),
+        header.get_destination_address()
+    );
+
+    println!("{:#?}", header);
+}