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/object/tests/round_trip/coff.rs

@@ -0,0 +1,58 @@
+use object::read::{Object, ObjectSection};
+use object::{read, write};
+use object::{
+    Architecture, BinaryFormat, Endianness, RelocationEncoding, RelocationFlags, RelocationKind,
+    SymbolFlags, SymbolKind, SymbolScope,
+};
+
+#[test]
+fn reloc_overflow() {
+    let mut object =
+        write::Object::new(BinaryFormat::Coff, Architecture::X86_64, Endianness::Little);
+    let text = object.section_id(write::StandardSection::Text);
+    object.append_section_data(text, &[0; 4], 4);
+    let symbol = object.add_symbol(write::Symbol {
+        name: b"f".to_vec(),
+        value: 0,
+        size: 4,
+        kind: SymbolKind::Text,
+        scope: SymbolScope::Linkage,
+        weak: false,
+        section: write::SymbolSection::Section(text),
+        flags: SymbolFlags::None,
+    });
+    for i in 0..0x10000 {
+        object
+            .add_relocation(
+                text,
+                write::Relocation {
+                    offset: i,
+                    symbol,
+                    addend: 0,
+                    flags: RelocationFlags::Generic {
+                        kind: RelocationKind::Absolute,
+                        encoding: RelocationEncoding::Generic,
+                        size: 64,
+                    },
+                },
+            )
+            .unwrap();
+    }
+    let bytes = object.write().unwrap();
+
+    //std::fs::write(&"reloc_overflow.o", &bytes).unwrap();
+
+    let object = read::File::parse(&*bytes).unwrap();
+    assert_eq!(object.format(), BinaryFormat::Coff);
+    assert_eq!(object.architecture(), Architecture::X86_64);
+
+    let section = object.sections().next().unwrap();
+    assert_eq!(section.name(), Ok(".text"));
+
+    let mut i = 0;
+    for (offset, _relocation) in section.relocations() {
+        assert_eq!(offset, i);
+        i += 1;
+    }
+    assert_eq!(i, 0x10000);
+}