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/windows-sys/src/core/literals.rs

@@ -0,0 +1,114 @@
+/// A literal UTF-8 string with a trailing null terminator.
+#[macro_export]
+macro_rules! s {
+    ($s:literal) => {
+        ::core::concat!($s, '\0').as_ptr()
+    };
+}
+
+/// A literal UTF-16 wide string with a trailing null terminator.
+#[macro_export]
+macro_rules! w {
+    ($s:literal) => {{
+        const INPUT: &[u8] = $s.as_bytes();
+        const OUTPUT_LEN: usize = $crate::core::utf16_len(INPUT) + 1;
+        const OUTPUT: &[u16; OUTPUT_LEN] = {
+            let mut buffer = [0; OUTPUT_LEN];
+            let mut input_pos = 0;
+            let mut output_pos = 0;
+            while let Some((mut code_point, new_pos)) = $crate::core::decode_utf8_char(INPUT, input_pos) {
+                input_pos = new_pos;
+                if code_point <= 0xffff {
+                    buffer[output_pos] = code_point as u16;
+                    output_pos += 1;
+                } else {
+                    code_point -= 0x10000;
+                    buffer[output_pos] = 0xd800 + (code_point >> 10) as u16;
+                    output_pos += 1;
+                    buffer[output_pos] = 0xdc00 + (code_point & 0x3ff) as u16;
+                    output_pos += 1;
+                }
+            }
+            &{ buffer }
+        };
+        OUTPUT.as_ptr()
+    }};
+}
+
+pub use s;
+pub use w;
+
+#[doc(hidden)]
+pub const fn decode_utf8_char(bytes: &[u8], mut pos: usize) -> Option<(u32, usize)> {
+    if bytes.len() == pos {
+        return None;
+    }
+    let ch = bytes[pos] as u32;
+    pos += 1;
+    if ch <= 0x7f {
+        return Some((ch, pos));
+    }
+    if (ch & 0xe0) == 0xc0 {
+        if bytes.len() - pos < 1 {
+            return None;
+        }
+        let ch2 = bytes[pos] as u32;
+        pos += 1;
+        if (ch2 & 0xc0) != 0x80 {
+            return None;
+        }
+        let result: u32 = ((ch & 0x1f) << 6) | (ch2 & 0x3f);
+        if result <= 0x7f {
+            return None;
+        }
+        return Some((result, pos));
+    }
+    if (ch & 0xf0) == 0xe0 {
+        if bytes.len() - pos < 2 {
+            return None;
+        }
+        let ch2 = bytes[pos] as u32;
+        pos += 1;
+        let ch3 = bytes[pos] as u32;
+        pos += 1;
+        if (ch2 & 0xc0) != 0x80 || (ch3 & 0xc0) != 0x80 {
+            return None;
+        }
+        let result = ((ch & 0x0f) << 12) | ((ch2 & 0x3f) << 6) | (ch3 & 0x3f);
+        if result <= 0x7ff || (0xd800 <= result && result <= 0xdfff) {
+            return None;
+        }
+        return Some((result, pos));
+    }
+    if (ch & 0xf8) == 0xf0 {
+        if bytes.len() - pos < 3 {
+            return None;
+        }
+        let ch2 = bytes[pos] as u32;
+        pos += 1;
+        let ch3 = bytes[pos] as u32;
+        pos += 1;
+        let ch4 = bytes[pos] as u32;
+        pos += 1;
+        if (ch2 & 0xc0) != 0x80 || (ch3 & 0xc0) != 0x80 || (ch4 & 0xc0) != 0x80 {
+            return None;
+        }
+        let result = ((ch & 0x07) << 18) | ((ch2 & 0x3f) << 12) | ((ch3 & 0x3f) << 6) | (ch4 & 0x3f);
+        if result <= 0xffff || 0x10ffff < result {
+            return None;
+        }
+        return Some((result, pos));
+    }
+    None
+}
+
+#[doc(hidden)]
+pub const fn utf16_len(bytes: &[u8]) -> usize {
+    let mut pos = 0;
+    let mut len = 0;
+    while let Some((code_point, new_pos)) = decode_utf8_char(bytes, pos) {
+        pos = new_pos;
+        len += if code_point <= 0xffff { 1 } else { 2 };
+    }
+    len
+}

vendor/windows-sys/src/core/mod.rs

@@ -0,0 +1,47 @@
+mod literals;
+
+#[doc(hidden)]
+pub use literals::*;
+
+pub type BOOL = i32;
+pub type HRESULT = i32;
+pub type PSTR = *mut u8;
+pub type PWSTR = *mut u16;
+pub type PCSTR = *const u8;
+pub type PCWSTR = *const u16;
+pub type BSTR = *const u16;
+pub type HSTRING = *mut core::ffi::c_void;
+
+#[repr(C)]
+#[derive(Copy, Clone, Default)]
+pub struct GUID {
+    pub data1: u32,
+    pub data2: u16,
+    pub data3: u16,
+    pub data4: [u8; 8],
+}
+
+impl GUID {
+    pub const fn from_u128(uuid: u128) -> Self {
+        Self { data1: (uuid >> 96) as u32, data2: (uuid >> 80 & 0xffff) as u16, data3: (uuid >> 64 & 0xffff) as u16, data4: (uuid as u64).to_be_bytes() }
+    }
+}
+
+pub const IID_IUnknown: GUID = GUID::from_u128(0x00000000_0000_0000_c000_000000000046);
+
+#[repr(C)]
+pub struct IUnknown_Vtbl {
+    pub QueryInterface: unsafe extern "system" fn(this: *mut core::ffi::c_void, iid: *const GUID, interface: *mut *mut core::ffi::c_void) -> HRESULT,
+    pub AddRef: unsafe extern "system" fn(this: *mut core::ffi::c_void) -> u32,
+    pub Release: unsafe extern "system" fn(this: *mut core::ffi::c_void) -> u32,
+}
+
+pub const IID_IInspectable: GUID = GUID::from_u128(0xaf86e2e0_b12d_4c6a_9c5a_d7aa65101e90);
+
+#[repr(C)]
+pub struct IInspectable_Vtbl {
+    pub base: IUnknown_Vtbl,
+    pub GetIids: unsafe extern "system" fn(this: *mut core::ffi::c_void, count: *mut u32, values: *mut *mut GUID) -> HRESULT,
+    pub GetRuntimeClassName: unsafe extern "system" fn(this: *mut core::ffi::c_void, value: *mut *mut core::ffi::c_void) -> HRESULT,
+    pub GetTrustLevel: unsafe extern "system" fn(this: *mut core::ffi::c_void, value: *mut i32) -> HRESULT,
+}