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/futures-core/src/lib.rs

@@ -0,0 +1,27 @@
+//! Core traits and types for asynchronous operations in Rust.
+
+#![no_std]
+#![doc(test(
+    no_crate_inject,
+    attr(
+        deny(warnings, rust_2018_idioms, single_use_lifetimes),
+        allow(dead_code, unused_assignments, unused_variables)
+    )
+))]
+#![warn(missing_docs, /* unsafe_op_in_unsafe_fn */)] // unsafe_op_in_unsafe_fn requires Rust 1.52
+
+#[cfg(feature = "alloc")]
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std;
+
+pub mod future;
+#[doc(no_inline)]
+pub use self::future::{FusedFuture, Future, TryFuture};
+
+pub mod stream;
+#[doc(no_inline)]
+pub use self::stream::{FusedStream, Stream, TryStream};
+
+#[macro_use]
+pub mod task;