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/chrono/Cargo.toml

@@ -0,0 +1,181 @@
+# 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 = "1.62.0"
+name = "chrono"
+version = "0.4.44"
+build = false
+include = [
+    "src/*",
+    "tests/*.rs",
+    "LICENSE.txt",
+    "CITATION.cff",
+]
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "Date and time library for Rust"
+homepage = "https://github.com/chronotope/chrono"
+documentation = "https://docs.rs/chrono/"
+readme = "README.md"
+keywords = [
+    "date",
+    "time",
+    "calendar",
+]
+categories = ["date-and-time"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/chronotope/chrono"
+
+[package.metadata.docs.rs]
+features = [
+    "arbitrary",
+    "rkyv",
+    "serde",
+    "unstable-locales",
+]
+rustdoc-args = [
+    "--cfg",
+    "docsrs",
+]
+
+[package.metadata.playground]
+features = ["serde"]
+
+[features]
+__internal_bench = []
+alloc = []
+clock = [
+    "winapi",
+    "iana-time-zone",
+    "now",
+]
+core-error = []
+default = [
+    "clock",
+    "std",
+    "oldtime",
+    "wasmbind",
+]
+defmt = [
+    "dep:defmt",
+    "pure-rust-locales?/defmt",
+]
+libc = []
+now = ["std"]
+oldtime = []
+rkyv = [
+    "dep:rkyv",
+    "rkyv/size_32",
+]
+rkyv-16 = [
+    "dep:rkyv",
+    "rkyv?/size_16",
+]
+rkyv-32 = [
+    "dep:rkyv",
+    "rkyv?/size_32",
+]
+rkyv-64 = [
+    "dep:rkyv",
+    "rkyv?/size_64",
+]
+rkyv-validation = ["rkyv?/validation"]
+std = ["alloc"]
+unstable-locales = ["pure-rust-locales"]
+wasmbind = [
+    "wasm-bindgen",
+    "js-sys",
+]
+winapi = ["windows-link"]
+
+[lib]
+name = "chrono"
+path = "src/lib.rs"
+
+[[test]]
+name = "dateutils"
+path = "tests/dateutils.rs"
+
+[[test]]
+name = "wasm"
+path = "tests/wasm.rs"
+
+[[test]]
+name = "win_bindings"
+path = "tests/win_bindings.rs"
+
+[dependencies.arbitrary]
+version = "1.0.0"
+features = ["derive"]
+optional = true
+
+[dependencies.defmt]
+version = "1.0.1"
+optional = true
+
+[dependencies.num-traits]
+version = "0.2"
+default-features = false
+
+[dependencies.pure-rust-locales]
+version = "0.8.2"
+optional = true
+
+[dependencies.rkyv]
+version = "0.7.43"
+optional = true
+default-features = false
+
+[dependencies.serde]
+version = "1.0.99"
+optional = true
+default-features = false
+
+[dev-dependencies.bincode]
+version = "1.3.0"
+
+[dev-dependencies.serde_derive]
+version = "1"
+default-features = false
+
+[dev-dependencies.serde_json]
+version = "1"
+
+[dev-dependencies.similar-asserts]
+version = "1.6.1"
+
+[dev-dependencies.windows-bindgen]
+version = "0.66"
+
+[target.'cfg(all(target_arch = "wasm32", not(any(target_os = "emscripten", target_os = "wasi"))))'.dependencies.js-sys]
+version = "0.3"
+optional = true
+
+[target.'cfg(all(target_arch = "wasm32", not(any(target_os = "emscripten", target_os = "wasi"))))'.dependencies.wasm-bindgen]
+version = "0.2"
+optional = true
+
+[target.'cfg(all(target_arch = "wasm32", not(any(target_os = "emscripten", target_os = "wasi"))))'.dev-dependencies.wasm-bindgen-test]
+version = "0.3"
+
+[target."cfg(unix)".dependencies.iana-time-zone]
+version = "0.1.45"
+features = ["fallback"]
+optional = true
+
+[target."cfg(windows)".dependencies.windows-link]
+version = "0.2"
+optional = true