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/enum-as-inner/README.md

@@ -0,0 +1,102 @@
+# enum-as-inner
+
+A deriving proc-macro for generating functions to automatically give access to the inner members of enum.
+
+## Basic unnamed field case
+
+The basic case is meant for single item enums, like:
+
+```rust
+use enum_as_inner::EnumAsInner;
+
+#[derive(Debug, EnumAsInner)]
+enum OneEnum {
+    One(u32),
+}
+```
+
+where the inner item can be retrieved with the `as_*()`/`as_*_mut()` or with the `into_*()` functions:
+
+```rust
+let one = OneEnum::One(1);
+
+assert_eq!(*one.as_one().unwrap(), 1);
+assert_eq!(one.into_one().unwrap(), 1);
+
+let mut one = OneEnum::One(2);
+
+assert_eq!(*one.as_one().unwrap(), 1);
+assert_eq!(*one.as_one_mut().unwrap(), 1);
+assert_eq!(one.into_one().unwrap(), 1);
+```
+
+where the result is either a reference for inner items or a tuple containing the inner items.
+
+## Unit case
+
+This will return true if enum's variant matches the expected type
+
+```rust
+use enum_as_inner::EnumAsInner;
+
+#[derive(EnumAsInner)]
+enum UnitVariants {
+    Zero,
+    One,
+    Two,
+}
+
+let unit = UnitVariants::Two;
+
+assert!(unit.is_two());
+```
+
+## Mutliple, unnamed field case
+
+This will return a tuple of the inner types:
+
+```rust
+use enum_as_inner::EnumAsInner;
+
+#[derive(Debug, EnumAsInner)]
+enum ManyVariants {
+    One(u32),
+    Two(u32, i32),
+    Three(bool, u32, i64),
+}
+```
+
+And can be accessed like:
+
+```rust
+let mut many = ManyVariants::Three(true, 1, 2);
+
+assert_eq!(many.as_three().unwrap(), (&true, &1_u32, &2_i64));
+assert_eq!(many.as_three_mut().unwrap(), (&mut true, &mut 1_u32, &mut 2_i64));
+assert_eq!(many.into_three().unwrap(), (true, 1_u32, 2_i64));
+```
+
+## Multiple, named field case
+
+This will return a tuple of the inner types, like the unnamed option:
+
+```rust
+use enum_as_inner::EnumAsInner;
+
+#[derive(Debug, EnumAsInner)]
+enum ManyVariants {
+    One{ one: u32 },
+    Two{ one: u32, two: i32 },
+    Three{ one: bool, two: u32, three: i64 },
+}
+```
+
+And can be accessed like:
+
+```rust
+let mut many = ManyVariants::Three{ one: true, two: 1, three: 2 };
+
+assert_eq!(many.as_three().unwrap(), (&true, &1_u32, &2_i64));
+assert_eq!(many.as_three_mut().unwrap(), (&mut true, &mut 1_u32, &mut 2_i64));
+assert_eq!(many.into_three().unwrap(), (true, 1_u32, 2_i64));
+```