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/thiserror-impl/src/prop.rs

@@ -0,0 +1,148 @@
+use crate::ast::{Enum, Field, Struct, Variant};
+use crate::unraw::MemberUnraw;
+use proc_macro2::Span;
+use syn::Type;
+
+impl Struct<'_> {
+    pub(crate) fn from_field(&self) -> Option<&Field> {
+        from_field(&self.fields)
+    }
+
+    pub(crate) fn source_field(&self) -> Option<&Field> {
+        source_field(&self.fields)
+    }
+
+    pub(crate) fn backtrace_field(&self) -> Option<&Field> {
+        backtrace_field(&self.fields)
+    }
+
+    pub(crate) fn distinct_backtrace_field(&self) -> Option<&Field> {
+        let backtrace_field = self.backtrace_field()?;
+        distinct_backtrace_field(backtrace_field, self.from_field())
+    }
+}
+
+impl Enum<'_> {
+    pub(crate) fn has_source(&self) -> bool {
+        self.variants
+            .iter()
+            .any(|variant| variant.source_field().is_some() || variant.attrs.transparent.is_some())
+    }
+
+    pub(crate) fn has_backtrace(&self) -> bool {
+        self.variants
+            .iter()
+            .any(|variant| variant.backtrace_field().is_some())
+    }
+
+    pub(crate) fn has_display(&self) -> bool {
+        self.attrs.display.is_some()
+            || self.attrs.transparent.is_some()
+            || self.attrs.fmt.is_some()
+            || self
+                .variants
+                .iter()
+                .any(|variant| variant.attrs.display.is_some() || variant.attrs.fmt.is_some())
+            || self
+                .variants
+                .iter()
+                .all(|variant| variant.attrs.transparent.is_some())
+    }
+}
+
+impl Variant<'_> {
+    pub(crate) fn from_field(&self) -> Option<&Field> {
+        from_field(&self.fields)
+    }
+
+    pub(crate) fn source_field(&self) -> Option<&Field> {
+        source_field(&self.fields)
+    }
+
+    pub(crate) fn backtrace_field(&self) -> Option<&Field> {
+        backtrace_field(&self.fields)
+    }
+
+    pub(crate) fn distinct_backtrace_field(&self) -> Option<&Field> {
+        let backtrace_field = self.backtrace_field()?;
+        distinct_backtrace_field(backtrace_field, self.from_field())
+    }
+}
+
+impl Field<'_> {
+    pub(crate) fn is_backtrace(&self) -> bool {
+        type_is_backtrace(self.ty)
+    }
+
+    pub(crate) fn source_span(&self) -> Span {
+        if let Some(source_attr) = &self.attrs.source {
+            source_attr.span
+        } else if let Some(from_attr) = &self.attrs.from {
+            from_attr.span
+        } else {
+            self.member.span()
+        }
+    }
+}
+
+fn from_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
+    for field in fields {
+        if field.attrs.from.is_some() {
+            return Some(field);
+        }
+    }
+    None
+}
+
+fn source_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
+    for field in fields {
+        if field.attrs.from.is_some() || field.attrs.source.is_some() {
+            return Some(field);
+        }
+    }
+    for field in fields {
+        match &field.member {
+            MemberUnraw::Named(ident) if ident == "source" => return Some(field),
+            _ => {}
+        }
+    }
+    None
+}
+
+fn backtrace_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
+    for field in fields {
+        if field.attrs.backtrace.is_some() {
+            return Some(field);
+        }
+    }
+    for field in fields {
+        if field.is_backtrace() {
+            return Some(field);
+        }
+    }
+    None
+}
+
+// The #[backtrace] field, if it is not the same as the #[from] field.
+fn distinct_backtrace_field<'a, 'b>(
+    backtrace_field: &'a Field<'b>,
+    from_field: Option<&Field>,
+) -> Option<&'a Field<'b>> {
+    if from_field.map_or(false, |from_field| {
+        from_field.member == backtrace_field.member
+    }) {
+        None
+    } else {
+        Some(backtrace_field)
+    }
+}
+
+fn type_is_backtrace(ty: &Type) -> bool {
+    let path = match ty {
+        Type::Path(ty) => &ty.path,
+        _ => return false,
+    };
+
+    let last = path.segments.last().unwrap();
+    last.ident == "Backtrace" && last.arguments.is_empty()
+}