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/src/array_of_tables.rs

@@ -0,0 +1,182 @@
+use std::iter::FromIterator;
+
+use crate::{Array, Item, Table};
+
+/// A top-level sequence of [`Table`]s, each under their own header
+#[derive(Clone, Debug, Default)]
+pub struct ArrayOfTables {
+    // Always Vec<Item::Table>, just `Item` to make `Index` work
+    pub(crate) span: Option<std::ops::Range<usize>>,
+    pub(crate) values: Vec<Item>,
+}
+
+/// Constructors
+///
+/// See also `FromIterator`
+impl ArrayOfTables {
+    /// Creates an empty array of tables.
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
+/// Formatting
+impl ArrayOfTables {
+    /// Convert to an inline array
+    pub fn into_array(mut self) -> Array {
+        for value in self.values.iter_mut() {
+            value.make_value();
+        }
+        let mut a = Array::with_vec(self.values);
+        a.fmt();
+        a
+    }
+
+    /// The location within the original document
+    ///
+    /// This generally requires a [`Document`][crate::Document].
+    pub fn span(&self) -> Option<std::ops::Range<usize>> {
+        self.span.clone()
+    }
+
+    pub(crate) fn despan(&mut self, input: &str) {
+        self.span = None;
+        for value in &mut self.values {
+            value.despan(input);
+        }
+    }
+}
+
+impl ArrayOfTables {
+    /// Returns an iterator over tables.
+    pub fn iter(&self) -> ArrayOfTablesIter<'_> {
+        Box::new(self.values.iter().filter_map(Item::as_table))
+    }
+
+    /// Returns an iterator over tables.
+    pub fn iter_mut(&mut self) -> ArrayOfTablesIterMut<'_> {
+        Box::new(self.values.iter_mut().filter_map(Item::as_table_mut))
+    }
+
+    /// Returns the length of the underlying Vec.
+    /// To get the actual number of items use `a.iter().count()`.
+    pub fn len(&self) -> usize {
+        self.values.len()
+    }
+
+    /// Returns true if `self.len() == 0`.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Removes all the tables.
+    pub fn clear(&mut self) {
+        self.values.clear();
+    }
+
+    /// Returns an optional reference to the table.
+    pub fn get(&self, index: usize) -> Option<&Table> {
+        self.values.get(index).and_then(Item::as_table)
+    }
+
+    /// Returns an optional mutable reference to the table.
+    pub fn get_mut(&mut self, index: usize) -> Option<&mut Table> {
+        self.values.get_mut(index).and_then(Item::as_table_mut)
+    }
+
+    /// Appends a table to the array.
+    pub fn push(&mut self, table: Table) {
+        self.values.push(Item::Table(table));
+    }
+
+    /// Inserts a table at the given index within the array, shifting all
+    /// tables after it to the right.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index > len`.
+    pub fn insert(&mut self, index: usize, table: Table) {
+        self.values.insert(index, Item::Table(table));
+    }
+
+    /// Removes a table with the given index.
+    pub fn remove(&mut self, index: usize) -> Table {
+        self.values
+            .remove(index)
+            .into_table()
+            .expect("cannot have any other item in an array-of-tables")
+    }
+
+    /// Retains only the elements specified by the `keep` predicate.
+    ///
+    /// In other words, remove all tables for which `keep(&table)` returns `false`.
+    ///
+    /// This method operates in place, visiting each element exactly once in the
+    /// original order, and preserves the order of the retained elements.
+    pub fn retain<F>(&mut self, mut keep: F)
+    where
+        F: FnMut(&Table) -> bool,
+    {
+        self.values
+            .retain(|item| item.as_table().map(&mut keep).unwrap_or(false));
+    }
+}
+
+/// An iterator type over [`ArrayOfTables`]'s [`Table`]s
+pub type ArrayOfTablesIter<'a> = Box<dyn Iterator<Item = &'a Table> + 'a>;
+/// An iterator type over [`ArrayOfTables`]'s [`Table`]s
+pub type ArrayOfTablesIterMut<'a> = Box<dyn Iterator<Item = &'a mut Table> + 'a>;
+/// An iterator type over [`ArrayOfTables`]'s [`Table`]s
+pub type ArrayOfTablesIntoIter = Box<dyn Iterator<Item = Table>>;
+
+impl Extend<Table> for ArrayOfTables {
+    fn extend<T: IntoIterator<Item = Table>>(&mut self, iter: T) {
+        for value in iter {
+            self.push(value);
+        }
+    }
+}
+
+impl FromIterator<Table> for ArrayOfTables {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = Table>,
+    {
+        let v = iter.into_iter().map(Item::Table);
+        Self {
+            values: v.collect(),
+            span: None,
+        }
+    }
+}
+
+impl IntoIterator for ArrayOfTables {
+    type Item = Table;
+    type IntoIter = ArrayOfTablesIntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        Box::new(
+            self.values
+                .into_iter()
+                .filter(|v| v.is_table())
+                .map(|v| v.into_table().unwrap()),
+        )
+    }
+}
+
+impl<'s> IntoIterator for &'s ArrayOfTables {
+    type Item = &'s Table;
+    type IntoIter = ArrayOfTablesIter<'s>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+#[cfg(feature = "display")]
+impl std::fmt::Display for ArrayOfTables {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        // HACK: Without the header, we don't really have a proper way of printing this
+        self.clone().into_array().fmt(f)
+    }
+}