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/file.rs

@@ -0,0 +1,166 @@
+use std::{io, mem};
+
+use windows_sys::Win32::Foundation::HANDLE;
+use windows_sys::Win32::Foundation::{GetLastError, FILETIME, NO_ERROR};
+use windows_sys::Win32::Storage::FileSystem::{
+    GetFileInformationByHandle, GetFileType, BY_HANDLE_FILE_INFORMATION,
+    FILE_ATTRIBUTE_HIDDEN,
+};
+
+use crate::AsHandleRef;
+
+/// Return various pieces of information about a file.
+///
+/// This includes information such as a file's size, unique identifier and
+/// time related fields.
+///
+/// This corresponds to calling [`GetFileInformationByHandle`].
+///
+/// [`GetFileInformationByHandle`]: https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-getfileinformationbyhandle
+pub fn information<H: AsHandleRef>(h: H) -> io::Result<Information> {
+    unsafe {
+        let mut info: BY_HANDLE_FILE_INFORMATION = mem::zeroed();
+        let rc = GetFileInformationByHandle(h.as_raw() as HANDLE, &mut info);
+        if rc == 0 {
+            return Err(io::Error::last_os_error());
+        };
+        Ok(Information(info))
+    }
+}
+
+/// Returns the file type of the given handle.
+///
+/// If there was a problem querying the file type, then an error is returned.
+///
+/// This corresponds to calling [`GetFileType`].
+///
+/// [`GetFileType`]: https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-getfiletype
+pub fn typ<H: AsHandleRef>(h: H) -> io::Result<Type> {
+    unsafe {
+        let rc = GetFileType(h.as_raw() as HANDLE);
+        if rc == 0 && GetLastError() != NO_ERROR {
+            return Err(io::Error::last_os_error());
+        }
+        Ok(Type(rc))
+    }
+}
+
+/// Returns true if and only if the given file attributes contain the
+/// `FILE_ATTRIBUTE_HIDDEN` attribute.
+pub fn is_hidden(file_attributes: u64) -> bool {
+    file_attributes & (FILE_ATTRIBUTE_HIDDEN as u64) > 0
+}
+
+/// Represents file information such as creation time, file size, etc.
+///
+/// This wraps a [`BY_HANDLE_FILE_INFORMATION`].
+///
+/// [`BY_HANDLE_FILE_INFORMATION`]: https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/ns-fileapi-_by_handle_file_information
+#[derive(Clone)]
+pub struct Information(BY_HANDLE_FILE_INFORMATION);
+
+impl Information {
+    /// Returns file attributes.
+    ///
+    /// This corresponds to `dwFileAttributes`.
+    pub fn file_attributes(&self) -> u64 {
+        self.0.dwFileAttributes as u64
+    }
+
+    /// Returns true if and only if this file information has the
+    /// `FILE_ATTRIBUTE_HIDDEN` attribute.
+    pub fn is_hidden(&self) -> bool {
+        is_hidden(self.file_attributes())
+    }
+
+    /// Return the creation time, if one exists.
+    ///
+    /// This corresponds to `ftCreationTime`.
+    pub fn creation_time(&self) -> Option<u64> {
+        filetime_to_u64(self.0.ftCreationTime)
+    }
+
+    /// Return the last access time, if one exists.
+    ///
+    /// This corresponds to `ftLastAccessTime`.
+    pub fn last_access_time(&self) -> Option<u64> {
+        filetime_to_u64(self.0.ftLastAccessTime)
+    }
+
+    /// Return the last write time, if one exists.
+    ///
+    /// This corresponds to `ftLastWriteTime`.
+    pub fn last_write_time(&self) -> Option<u64> {
+        filetime_to_u64(self.0.ftLastWriteTime)
+    }
+
+    /// Return the serial number of the volume that the file is on.
+    ///
+    /// This corresponds to `dwVolumeSerialNumber`.
+    pub fn volume_serial_number(&self) -> u64 {
+        self.0.dwVolumeSerialNumber as u64
+    }
+
+    /// Return the file size, in bytes.
+    ///
+    /// This corresponds to `nFileSizeHigh` and `nFileSizeLow`.
+    pub fn file_size(&self) -> u64 {
+        ((self.0.nFileSizeHigh as u64) << 32) | (self.0.nFileSizeLow as u64)
+    }
+
+    /// Return the number of links to this file.
+    ///
+    /// This corresponds to `nNumberOfLinks`.
+    pub fn number_of_links(&self) -> u64 {
+        self.0.nNumberOfLinks as u64
+    }
+
+    /// Return the index of this file. The index of a file is a purpotedly
+    /// unique identifier for a file within a particular volume.
+    pub fn file_index(&self) -> u64 {
+        ((self.0.nFileIndexHigh as u64) << 32) | (self.0.nFileIndexLow as u64)
+    }
+}
+
+/// Represents a Windows file type.
+///
+/// This wraps the result of [`GetFileType`].
+///
+/// [`GetFileType`]: https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-getfiletype
+#[derive(Clone)]
+pub struct Type(u32);
+
+impl Type {
+    /// Returns true if this type represents a character file, which is
+    /// typically an LPT device or a console.
+    pub fn is_char(&self) -> bool {
+        self.0 == ::windows_sys::Win32::Storage::FileSystem::FILE_TYPE_CHAR
+    }
+
+    /// Returns true if this type represents a disk file.
+    pub fn is_disk(&self) -> bool {
+        self.0 == ::windows_sys::Win32::Storage::FileSystem::FILE_TYPE_DISK
+    }
+
+    /// Returns true if this type represents a sock, named pipe or an
+    /// anonymous pipe.
+    pub fn is_pipe(&self) -> bool {
+        self.0 == ::windows_sys::Win32::Storage::FileSystem::FILE_TYPE_PIPE
+    }
+
+    /// Returns true if this type is not known.
+    ///
+    /// Note that this never corresponds to a failure.
+    pub fn is_unknown(&self) -> bool {
+        self.0 == ::windows_sys::Win32::Storage::FileSystem::FILE_TYPE_UNKNOWN
+    }
+}
+
+fn filetime_to_u64(t: FILETIME) -> Option<u64> {
+    let v = ((t.dwHighDateTime as u64) << 32) | (t.dwLowDateTime as u64);
+    if v == 0 {
+        None
+    } else {
+        Some(v)
+    }
+}