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/src/impls/arrays.rs

@@ -0,0 +1,100 @@
+use super::*;
+use crate::export;
+
+macro_rules! arrays {
+    ( $($len:literal $fmt:literal,)+ ) => {
+        impl<T, const N: usize> Format for [T; N]
+        where
+            T: Format
+        {
+            default_format!();
+
+            #[inline]
+            fn _format_tag() -> Str {
+                match N {
+                    $(
+                        $len => internp!($fmt),
+                    )+
+                    _ => internp!("{=[?]}"),
+                }
+            }
+
+            #[inline]
+            fn _format_data(&self) {
+                match N {
+                    $( $len )|+ => export::fmt_array(self),
+                    _ => export::fmt_slice(self),
+                }
+            }
+        }
+    };
+}
+
+arrays! {
+    0 "{=[?;0]}",
+    1 "{=[?;1]}",
+    2 "{=[?;2]}",
+    3 "{=[?;3]}",
+    4 "{=[?;4]}",
+    5 "{=[?;5]}",
+    6 "{=[?;6]}",
+    7 "{=[?;7]}",
+    8 "{=[?;8]}",
+    9 "{=[?;9]}",
+    10 "{=[?;10]}",
+    11 "{=[?;11]}",
+    12 "{=[?;12]}",
+    13 "{=[?;13]}",
+    14 "{=[?;14]}",
+    15 "{=[?;15]}",
+    16 "{=[?;16]}",
+    17 "{=[?;17]}",
+    18 "{=[?;18]}",
+    19 "{=[?;19]}",
+    20 "{=[?;20]}",
+    21 "{=[?;21]}",
+    22 "{=[?;22]}",
+    23 "{=[?;23]}",
+    24 "{=[?;24]}",
+    25 "{=[?;25]}",
+    26 "{=[?;26]}",
+    27 "{=[?;27]}",
+    28 "{=[?;28]}",
+    29 "{=[?;29]}",
+    30 "{=[?;30]}",
+    31 "{=[?;31]}",
+    32 "{=[?;32]}",
+    64 "{=[?;64]}",
+    128 "{=[?;128]}",
+    256 "{=[?;256]}",
+    512 "{=[?;512]}",
+    1024 "{=[?;1024]}",
+    2048 "{=[?;2048]}",
+    4096 "{=[?;4096]}",
+    8192 "{=[?;8192]}",
+    16384 "{=[?;16384]}",
+    32768 "{=[?;32768]}",
+    65536 "{=[?;65536]}",
+    131072 "{=[?;131072]}",
+    262144 "{=[?;262144]}",
+    524288 "{=[?;524288]}",
+    1048576 "{=[?;1048576]}",
+    2097152 "{=[?;2097152]}",
+    4194304 "{=[?;4194304]}",
+    8388608 "{=[?;8388608]}",
+    16777216 "{=[?;16777216]}",
+    33554432 "{=[?;33554432]}",
+    67108864 "{=[?;67108864]}",
+    134217728 "{=[?;134217728]}",
+    268435456 "{=[?;268435456]}",
+    536870912 "{=[?;536870912]}",
+    1073741824 "{=[?;1073741824]}",
+    100 "{=[?;100]}",
+    1000 "{=[?;1000]}",
+    10000 "{=[?;10000]}",
+    100000 "{=[?;100000]}",
+    1000000 "{=[?;1000000]}",
+    10000000 "{=[?;10000000]}",
+    100000000 "{=[?;100000000]}",
+    1000000000 "{=[?;1000000000]}",
+}