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/winapi-util/src/sysinfo.rs

@@ -0,0 +1,161 @@
+use std::{ffi::OsString, io};
+
+use windows_sys::Win32::System::SystemInformation::{
+    GetComputerNameExW, COMPUTER_NAME_FORMAT,
+};
+
+/// The type of name to be retrieved by [`get_computer_name`].
+#[derive(Clone, Copy, Debug)]
+#[non_exhaustive]
+pub enum ComputerNameKind {
+    /// The name of the DNS domain assigned to the local computer. If the local
+    /// computer is a node in a cluster, lpBuffer receives the DNS domain name
+    /// of the cluster virtual server.
+    DnsDomain,
+    /// The fully qualified DNS name that uniquely identifies the local
+    /// computer. This name is a combination of the DNS host name and the DNS
+    /// domain name, using the form HostName.DomainName. If the local computer
+    /// is a node in a cluster, lpBuffer receives the fully qualified DNS name
+    /// of the cluster virtual server.
+    DnsFullyQualified,
+    /// The DNS host name of the local computer. If the local computer is a
+    /// node in a cluster, lpBuffer receives the DNS host name of the cluster
+    /// virtual server.
+    DnsHostname,
+    /// The NetBIOS name of the local computer. If the local computer is a node
+    /// in a cluster, lpBuffer receives the NetBIOS name of the cluster virtual
+    /// server.
+    NetBios,
+    /// The name of the DNS domain assigned to the local computer. If the local
+    /// computer is a node in a cluster, lpBuffer receives the DNS domain name
+    /// of the local computer, not the name of the cluster virtual server.
+    PhysicalDnsDomain,
+    /// The fully qualified DNS name that uniquely identifies the computer. If
+    /// the local computer is a node in a cluster, lpBuffer receives the fully
+    /// qualified DNS name of the local computer, not the name of the cluster
+    /// virtual server.
+    ///
+    /// The fully qualified DNS name is a combination of the DNS host name and
+    /// the DNS domain name, using the form HostName.DomainName.
+    PhysicalDnsFullyQualified,
+    /// The DNS host name of the local computer. If the local computer is a
+    /// node in a cluster, lpBuffer receives the DNS host name of the local
+    /// computer, not the name of the cluster virtual server.
+    PhysicalDnsHostname,
+    /// The NetBIOS name of the local computer. If the local computer is a node
+    /// in a cluster, lpBuffer receives the NetBIOS name of the local computer,
+    /// not the name of the cluster virtual server.
+    PhysicalNetBios,
+}
+
+impl ComputerNameKind {
+    fn to_format(&self) -> COMPUTER_NAME_FORMAT {
+        use self::ComputerNameKind::*;
+        use windows_sys::Win32::System::SystemInformation;
+
+        match *self {
+            DnsDomain => SystemInformation::ComputerNameDnsDomain,
+            DnsFullyQualified => {
+                SystemInformation::ComputerNameDnsFullyQualified
+            }
+            DnsHostname => SystemInformation::ComputerNameDnsHostname,
+            NetBios => SystemInformation::ComputerNameNetBIOS,
+            PhysicalDnsDomain => {
+                SystemInformation::ComputerNamePhysicalDnsDomain
+            }
+            PhysicalDnsFullyQualified => {
+                SystemInformation::ComputerNamePhysicalDnsFullyQualified
+            }
+            PhysicalDnsHostname => {
+                SystemInformation::ComputerNamePhysicalDnsHostname
+            }
+            PhysicalNetBios => SystemInformation::ComputerNamePhysicalNetBIOS,
+        }
+    }
+}
+/// Retrieves a NetBIOS or DNS name associated with the local computer.
+///
+/// The names are established at system startup, when the system reads them
+/// from the registry.
+///
+/// This corresponds to calling [`GetComputerNameExW`].
+///
+/// [`GetComputerNameExW`]: https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getcomputernameexw
+pub fn get_computer_name(kind: ComputerNameKind) -> io::Result<OsString> {
+    use std::os::windows::ffi::OsStringExt;
+
+    let format = kind.to_format();
+    let mut len1 = 0;
+    // SAFETY: As documented, we call this with a null pointer which will in
+    // turn cause this routine to write the required buffer size fo `len1`.
+    // Also, we explicitly ignore the return value since we expect this call to
+    // fail given that the destination buffer is too small by design.
+    let _ =
+        unsafe { GetComputerNameExW(format, std::ptr::null_mut(), &mut len1) };
+
+    let len = match usize::try_from(len1) {
+        Ok(len) => len,
+        Err(_) => {
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                "GetComputerNameExW buffer length overflowed usize",
+            ))
+        }
+    };
+    let mut buf = vec![0; len];
+    let mut len2 = len1;
+    // SAFETY: We pass a valid pointer to an appropriately sized Vec<u16>.
+    let rc =
+        unsafe { GetComputerNameExW(format, buf.as_mut_ptr(), &mut len2) };
+    if rc == 0 {
+        return Err(io::Error::last_os_error());
+    }
+    // Apparently, the subsequent call writes the number of characters written
+    // to the buffer to `len2` but not including the NUL terminator. Notice
+    // that in the first call above, the length written to `len1` *does*
+    // include the NUL terminator. Therefore, we expect `len1` to be at least
+    // one greater than `len2`. If not, then something weird has happened and
+    // we report an error.
+    if len1 <= len2 {
+        let msg = format!(
+            "GetComputerNameExW buffer length mismatch, \
+             expected length strictly less than {} \
+             but got {}",
+            len1, len2,
+        );
+        return Err(io::Error::new(io::ErrorKind::Other, msg));
+    }
+    let len = usize::try_from(len2).expect("len1 fits implies len2 fits");
+    Ok(OsString::from_wide(&buf[..len]))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // This test doesn't really check anything other than that we can
+    // successfully query all kinds of computer names. We just print them out
+    // since there aren't really any properties about the names that we can
+    // assert.
+    //
+    // We specifically run this test in CI with --nocapture so that we can see
+    // the output.
+    #[test]
+    fn itworks() {
+        let kinds = [
+            ComputerNameKind::DnsDomain,
+            ComputerNameKind::DnsFullyQualified,
+            ComputerNameKind::DnsHostname,
+            ComputerNameKind::NetBios,
+            ComputerNameKind::PhysicalDnsDomain,
+            ComputerNameKind::PhysicalDnsFullyQualified,
+            ComputerNameKind::PhysicalDnsHostname,
+            ComputerNameKind::PhysicalNetBios,
+        ];
+        for kind in kinds {
+            let result = get_computer_name(kind);
+            let name = result.unwrap();
+            println!("{kind:?}: {name:?}");
+        }
+    }
+}