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/defmt-macros/src/function_like/assert_binop.rs

@@ -0,0 +1,90 @@
+use defmt_parser::Level;
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, punctuated::Punctuated};
+
+use crate::{construct, function_like::log};
+
+use self::args::Args;
+
+mod args;
+
+pub(crate) fn eq(args: TokenStream) -> TokenStream {
+    expand(args, BinOp::Eq)
+}
+
+pub(crate) fn ne(args: TokenStream) -> TokenStream {
+    expand(args, BinOp::Ne)
+}
+
+fn expand(args: TokenStream, binop: BinOp) -> TokenStream {
+    let args = parse_macro_input!(args as Args);
+
+    let left = args.left;
+    let right = args.right;
+
+    let mut formatting_args = Punctuated::new();
+
+    let extra_string = if let Some(log_args) = args.log_args {
+        if let Some(args) = log_args.formatting_args {
+            formatting_args.extend(args);
+        }
+        format!(": {}", log_args.format_string.value())
+    } else {
+        String::new()
+    };
+
+    let vals = match binop {
+        BinOp::Eq => &["left_val", "right_val"][..],
+        BinOp::Ne => &["left_val"][..],
+    };
+
+    for val in vals {
+        formatting_args.push(construct::variable(val));
+    }
+
+    let panic_msg = match binop {
+        BinOp::Eq => format!(
+            "panicked at 'assertion failed: `(left == right)`{}'
+ left: `{{:?}}`
+right: `{{:?}}`",
+            extra_string
+        ),
+        BinOp::Ne => format!(
+            "panicked at 'assertion failed: `(left != right)`{}'
+left/right: `{{:?}}`",
+            extra_string
+        ),
+    };
+
+    let log_args = log::Args {
+        format_string: construct::string_literal(&panic_msg),
+        formatting_args: Some(formatting_args),
+    };
+    let log_stmt = log::expand_parsed(Level::Error, log_args);
+
+    let mut cond = quote!(*left_val == *right_val);
+    if binop == BinOp::Eq {
+        cond = quote!(!(#cond));
+    }
+
+    quote!(
+        // evaluate arguments first
+        match (&(#left), &(#right)) {
+            (left_val, right_val) => {
+                // following `core::assert_eq!`
+                if #cond {
+                    #log_stmt;
+                    defmt::export::panic()
+                }
+            }
+        }
+    )
+    .into()
+}
+
+#[derive(PartialEq)]
+enum BinOp {
+    Eq,
+    Ne,
+}