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/toml_edit-0.22.27/src/document.rs

@@ -0,0 +1,235 @@
+use std::str::FromStr;
+
+use crate::table::Iter;
+use crate::{Item, RawString, Table};
+
+/// The root TOML [`Table`], containing [`Key`][crate::Key]/[`Value`][crate::Value] pairs and all other logic [`Table`]s
+#[derive(Debug, Clone)]
+pub struct ImDocument<S> {
+    pub(crate) root: Item,
+    // Trailing comments and whitespaces
+    pub(crate) trailing: RawString,
+    pub(crate) raw: S,
+}
+
+impl ImDocument<&'static str> {
+    /// Creates an empty document
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
+#[cfg(feature = "parse")]
+impl<S: AsRef<str>> ImDocument<S> {
+    /// Parse a TOML document
+    pub fn parse(raw: S) -> Result<Self, crate::TomlError> {
+        crate::parser::parse_document(raw)
+    }
+}
+
+impl<S: AsRef<str>> ImDocument<S> {
+    /// # Panics
+    ///
+    /// If run on a [`DocumentMut`] not generated by the parser
+    pub(crate) fn despan(&mut self) {
+        self.root.despan(self.raw.as_ref());
+        self.trailing.despan(self.raw.as_ref());
+    }
+}
+
+impl<S> ImDocument<S> {
+    /// Returns a reference to the root item.
+    pub fn as_item(&self) -> &Item {
+        &self.root
+    }
+
+    /// Returns the root item.
+    pub fn into_item(self) -> Item {
+        self.root
+    }
+
+    /// Returns a reference to the root table.
+    pub fn as_table(&self) -> &Table {
+        self.root.as_table().expect("root should always be a table")
+    }
+
+    /// Returns the root table.
+    pub fn into_table(self) -> Table {
+        self.root
+            .into_table()
+            .expect("root should always be a table")
+    }
+
+    /// Returns an iterator over the root table.
+    pub fn iter(&self) -> Iter<'_> {
+        self.as_table().iter()
+    }
+
+    /// Whitespace after last element
+    pub fn trailing(&self) -> &RawString {
+        &self.trailing
+    }
+}
+
+impl<S: AsRef<str>> ImDocument<S> {
+    /// Access the raw, unparsed document
+    pub fn raw(&self) -> &str {
+        self.raw.as_ref()
+    }
+}
+
+impl<S: AsRef<str>> ImDocument<S> {
+    /// Allow editing of the [`DocumentMut`]
+    pub fn into_mut(mut self) -> DocumentMut {
+        self.despan();
+        DocumentMut {
+            root: self.root,
+            trailing: self.trailing,
+        }
+    }
+}
+
+impl Default for ImDocument<&'static str> {
+    fn default() -> Self {
+        Self {
+            root: Item::Table(Table::with_pos(Some(0))),
+            trailing: Default::default(),
+            raw: "",
+        }
+    }
+}
+
+#[cfg(feature = "parse")]
+impl FromStr for ImDocument<String> {
+    type Err = crate::TomlError;
+
+    /// Parses a document from a &str
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Self::parse(s.to_owned())
+    }
+}
+
+impl<S> std::ops::Deref for ImDocument<S> {
+    type Target = Table;
+
+    fn deref(&self) -> &Self::Target {
+        self.as_table()
+    }
+}
+
+/// The editable root TOML [`Table`], containing [`Key`][crate::Key]/[`Value`][crate::Value] pairs and all other logic [`Table`]s
+#[derive(Debug, Clone)]
+pub struct DocumentMut {
+    pub(crate) root: Item,
+    // Trailing comments and whitespaces
+    pub(crate) trailing: RawString,
+}
+
+impl DocumentMut {
+    /// Creates an empty document
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    /// Returns a reference to the root item.
+    pub fn as_item(&self) -> &Item {
+        &self.root
+    }
+
+    /// Returns a mutable reference to the root item.
+    pub fn as_item_mut(&mut self) -> &mut Item {
+        &mut self.root
+    }
+
+    /// Returns the root item.
+    pub fn into_item(self) -> Item {
+        self.root
+    }
+
+    /// Returns a reference to the root table.
+    pub fn as_table(&self) -> &Table {
+        self.root.as_table().expect("root should always be a table")
+    }
+
+    /// Returns a mutable reference to the root table.
+    pub fn as_table_mut(&mut self) -> &mut Table {
+        self.root
+            .as_table_mut()
+            .expect("root should always be a table")
+    }
+
+    /// Returns the root table.
+    pub fn into_table(self) -> Table {
+        self.root
+            .into_table()
+            .expect("root should always be a table")
+    }
+
+    /// Returns an iterator over the root table.
+    pub fn iter(&self) -> Iter<'_> {
+        self.as_table().iter()
+    }
+
+    /// Set whitespace after last element
+    pub fn set_trailing(&mut self, trailing: impl Into<RawString>) {
+        self.trailing = trailing.into();
+    }
+
+    /// Whitespace after last element
+    pub fn trailing(&self) -> &RawString {
+        &self.trailing
+    }
+}
+
+impl Default for DocumentMut {
+    fn default() -> Self {
+        Self {
+            root: Item::Table(Table::with_pos(Some(0))),
+            trailing: Default::default(),
+        }
+    }
+}
+
+#[cfg(feature = "parse")]
+impl FromStr for DocumentMut {
+    type Err = crate::TomlError;
+
+    /// Parses a document from a &str
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let im = ImDocument::from_str(s)?;
+        Ok(im.into_mut())
+    }
+}
+
+impl std::ops::Deref for DocumentMut {
+    type Target = Table;
+
+    fn deref(&self) -> &Self::Target {
+        self.as_table()
+    }
+}
+
+impl std::ops::DerefMut for DocumentMut {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.as_table_mut()
+    }
+}
+
+impl From<Table> for DocumentMut {
+    fn from(root: Table) -> Self {
+        Self {
+            root: Item::Table(root),
+            ..Default::default()
+        }
+    }
+}
+
+#[test]
+#[cfg(feature = "parse")]
+#[cfg(feature = "display")]
+fn default_roundtrip() {
+    DocumentMut::default()
+        .to_string()
+        .parse::<DocumentMut>()
+        .unwrap();
+}