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/read/coff.rs

@@ -0,0 +1,23 @@
+use object::{pe, read, Object, ObjectSection};
+use std::fs;
+use std::path::PathBuf;
+
+#[cfg(feature = "coff")]
+#[test]
+fn coff_extended_relocations() {
+    let path_to_obj: PathBuf = ["testfiles", "coff", "relocs_overflow.o"].iter().collect();
+    let contents = fs::read(path_to_obj).expect("Could not read relocs_overflow.o");
+    let file =
+        read::coff::CoffFile::<_>::parse(&contents[..]).expect("Could not parse relocs_overflow.o");
+    let code_section = file
+        .section_by_name(".text")
+        .expect("Could not find .text section in relocs_overflow.o");
+    match code_section.flags() {
+        object::SectionFlags::Coff { characteristics } => {
+            assert!(characteristics & pe::IMAGE_SCN_LNK_NRELOC_OVFL != 0)
+        }
+        _ => panic!("Invalid section flags flavour."),
+    };
+    let relocations = code_section.relocations().collect::<Vec<_>>();
+    assert_eq!(relocations.len(), 65536);
+}