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/ident_case/src/lib.rs

@@ -0,0 +1,168 @@
+//! Crate for changing case of Rust identifiers.
+//!
+//! # Features
+//! * Supports `snake_case`, `lowercase`, `camelCase`, 
+//!   `PascalCase`, `SCREAMING_SNAKE_CASE`, and `kebab-case`
+//! * Rename variants, and fields
+//! 
+//! # Examples
+//! ```rust
+//! use ident_case::RenameRule;
+//!
+//! assert_eq!("helloWorld", RenameRule::CamelCase.apply_to_field("hello_world"));
+//!
+//! assert_eq!("i_love_serde", RenameRule::SnakeCase.apply_to_variant("ILoveSerde"));
+//! ```
+
+// Copyright 2017 Serde Developers
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::ascii::AsciiExt;
+use std::str::FromStr;
+
+use self::RenameRule::*;
+
+/// A casing rule for renaming Rust identifiers.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum RenameRule {
+    /// No-op rename rule.
+    None,
+    /// Rename direct children to "lowercase" style.
+    LowerCase,
+    /// Rename direct children to "PascalCase" style, as typically used for enum variants.
+    PascalCase,
+    /// Rename direct children to "camelCase" style.
+    CamelCase,
+    /// Rename direct children to "snake_case" style, as commonly used for fields.
+    SnakeCase,
+    /// Rename direct children to "SCREAMING_SNAKE_CASE" style, as commonly used for constants.
+    ScreamingSnakeCase,
+    /// Rename direct children to "kebab-case" style.
+    KebabCase,
+}
+
+impl RenameRule {
+    /// Change case of a `PascalCase` variant.
+    pub fn apply_to_variant<S: AsRef<str>>(&self, variant: S) -> String {
+        
+        let variant = variant.as_ref();
+        match *self {
+            None | PascalCase => variant.to_owned(),
+            LowerCase => variant.to_ascii_lowercase(),
+            CamelCase => variant[..1].to_ascii_lowercase() + &variant[1..],
+            SnakeCase => {
+                let mut snake = String::new();
+                for (i, ch) in variant.char_indices() {
+                    if i > 0 && ch.is_uppercase() {
+                        snake.push('_');
+                    }
+                    snake.push(ch.to_ascii_lowercase());
+                }
+                snake
+            }
+            ScreamingSnakeCase => SnakeCase.apply_to_variant(variant).to_ascii_uppercase(),
+            KebabCase => SnakeCase.apply_to_variant(variant).replace('_', "-"),
+        }
+    }
+
+    /// Change case of a `snake_case` field.
+    pub fn apply_to_field<S: AsRef<str>>(&self, field: S) -> String {
+        
+        let field = field.as_ref();
+        match *self {
+            None | LowerCase | SnakeCase => field.to_owned(),
+            PascalCase => {
+                let mut pascal = String::new();
+                let mut capitalize = true;
+                for ch in field.chars() {
+                    if ch == '_' {
+                        capitalize = true;
+                    } else if capitalize {
+                        pascal.push(ch.to_ascii_uppercase());
+                        capitalize = false;
+                    } else {
+                        pascal.push(ch);
+                    }
+                }
+                pascal
+            }
+            CamelCase => {
+                let pascal = PascalCase.apply_to_field(field);
+                pascal[..1].to_ascii_lowercase() + &pascal[1..]
+            }
+            ScreamingSnakeCase => field.to_ascii_uppercase(),
+            KebabCase => field.replace('_', "-"),
+        }
+    }
+}
+
+impl FromStr for RenameRule {
+    type Err = ();
+
+    fn from_str(rename_all_str: &str) -> Result<Self, Self::Err> {
+        match rename_all_str {
+            "lowercase" => Ok(LowerCase),
+            "PascalCase" => Ok(PascalCase),
+            "camelCase" => Ok(CamelCase),
+            "snake_case" => Ok(SnakeCase),
+            "SCREAMING_SNAKE_CASE" => Ok(ScreamingSnakeCase),
+            "kebab-case" => Ok(KebabCase),
+            _ => Err(()),
+        }
+    }
+}
+
+impl Default for RenameRule {
+    fn default() -> Self {
+        RenameRule::None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::RenameRule::*;
+
+    #[test]
+    fn rename_variants() {
+        for &(original, lower, camel, snake, screaming, kebab) in
+            &[
+                ("Outcome", "outcome", "outcome", "outcome", "OUTCOME", "outcome"),
+                ("VeryTasty", "verytasty", "veryTasty", "very_tasty", "VERY_TASTY", "very-tasty"),
+                ("A", "a", "a", "a", "A", "a"),
+                ("Z42", "z42", "z42", "z42", "Z42", "z42"),
+            ] {
+            assert_eq!(None.apply_to_variant(original), original);
+            assert_eq!(LowerCase.apply_to_variant(original), lower);
+            assert_eq!(PascalCase.apply_to_variant(original), original);
+            assert_eq!(CamelCase.apply_to_variant(original), camel);
+            assert_eq!(SnakeCase.apply_to_variant(original), snake);
+            assert_eq!(ScreamingSnakeCase.apply_to_variant(original), screaming);
+            assert_eq!(KebabCase.apply_to_variant(original), kebab);
+        }
+    }
+
+    #[test]
+    fn rename_fields() {
+        for &(original, pascal, camel, screaming, kebab) in
+            &[
+                ("outcome", "Outcome", "outcome", "OUTCOME", "outcome"),
+                ("very_tasty", "VeryTasty", "veryTasty", "VERY_TASTY", "very-tasty"),
+                ("_leading_under", "LeadingUnder", "leadingUnder", "_LEADING_UNDER", "-leading-under"),
+                ("double__under", "DoubleUnder", "doubleUnder", "DOUBLE__UNDER", "double--under"),
+                ("a", "A", "a", "A", "a"),
+                ("z42", "Z42", "z42", "Z42", "z42"),
+            ] {
+            assert_eq!(None.apply_to_field(original), original);
+            assert_eq!(PascalCase.apply_to_field(original), pascal);
+            assert_eq!(CamelCase.apply_to_field(original), camel);
+            assert_eq!(SnakeCase.apply_to_field(original), original);
+            assert_eq!(ScreamingSnakeCase.apply_to_field(original), screaming);
+            assert_eq!(KebabCase.apply_to_field(original), kebab);
+        }
+    }
+}