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/half/Cargo.toml

@@ -0,0 +1,137 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2021"
+rust-version = "1.81"
+name = "half"
+version = "2.7.1"
+authors = ["Kathryn Long <squeeself@gmail.com>"]
+build = false
+exclude = [
+    ".git*",
+    ".editorconfig",
+    ".circleci",
+]
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "Half-precision floating point f16 and bf16 types for Rust implementing the IEEE 754-2008 standard binary16 and bfloat16 types."
+readme = "README.md"
+keywords = [
+    "f16",
+    "bfloat16",
+    "no_std",
+]
+categories = [
+    "no-std",
+    "data-structures",
+    "encoding",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/VoidStarKat/half-rs"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = [
+    "--cfg",
+    "docsrs",
+]
+
+[features]
+alloc = []
+default = ["std"]
+nightly = []
+rand_distr = [
+    "dep:rand",
+    "dep:rand_distr",
+]
+std = ["alloc"]
+use-intrinsics = []
+zerocopy = []
+
+[lib]
+name = "half"
+path = "src/lib.rs"
+
+[[bench]]
+name = "convert"
+path = "benches/convert.rs"
+harness = false
+
+[dependencies.arbitrary]
+version = "1.4.1"
+features = ["derive"]
+optional = true
+
+[dependencies.bytemuck]
+version = "1.4.1"
+features = ["derive"]
+optional = true
+default-features = false
+
+[dependencies.cfg-if]
+version = "1.0.0"
+
+[dependencies.num-traits]
+version = "0.2.16"
+features = ["libm"]
+optional = true
+default-features = false
+
+[dependencies.rand]
+version = "0.9.0"
+features = ["thread_rng"]
+optional = true
+default-features = false
+
+[dependencies.rand_distr]
+version = "0.5.0"
+optional = true
+default-features = false
+
+[dependencies.rkyv]
+version = "0.8.0"
+optional = true
+
+[dependencies.serde]
+version = "1.0"
+features = ["derive"]
+optional = true
+default-features = false
+
+[dependencies.zerocopy]
+version = "0.8.26"
+features = [
+    "derive",
+    "simd",
+]
+default-features = false
+
+[dev-dependencies.criterion]
+version = "0.5"
+
+[dev-dependencies.crunchy]
+version = "0.2.2"
+
+[dev-dependencies.quickcheck]
+version = "1.0"
+
+[dev-dependencies.quickcheck_macros]
+version = "1.0"
+
+[dev-dependencies.rand]
+version = "0.9.0"
+
+[target.'cfg(target_arch = "spirv")'.dependencies.crunchy]
+version = "0.2.2"