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/ahash/Cargo.toml

@@ -0,0 +1,183 @@
+# 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 = "2018"
+rust-version = "1.60.0"
+name = "ahash"
+version = "0.8.12"
+authors = ["Tom Kaitchuck <Tom.Kaitchuck@gmail.com>"]
+build = "build.rs"
+exclude = [
+    "/smhasher",
+    "/benchmark_tools",
+]
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "A non-cryptographic hash function using AES-NI for high performance"
+documentation = "https://docs.rs/ahash"
+readme = "README.md"
+keywords = [
+    "hash",
+    "hasher",
+    "hashmap",
+    "aes",
+    "no-std",
+]
+categories = [
+    "algorithms",
+    "data-structures",
+    "no-std",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/tkaitchuck/ahash"
+
+[package.metadata.docs.rs]
+features = ["std"]
+rustc-args = [
+    "-C",
+    "target-feature=+aes",
+]
+rustdoc-args = [
+    "-C",
+    "target-feature=+aes",
+]
+
+[profile.bench]
+opt-level = 3
+lto = "fat"
+codegen-units = 1
+debug = 0
+debug-assertions = false
+
+[profile.release]
+opt-level = 3
+lto = "fat"
+codegen-units = 1
+debug = 0
+debug-assertions = false
+
+[profile.test]
+opt-level = 2
+lto = "fat"
+
+[lib]
+name = "ahash"
+path = "src/lib.rs"
+test = true
+doctest = true
+bench = true
+doc = true
+
+[[test]]
+name = "bench"
+path = "tests/bench.rs"
+
+[[test]]
+name = "map_tests"
+path = "tests/map_tests.rs"
+
+[[test]]
+name = "nopanic"
+path = "tests/nopanic.rs"
+
+[[bench]]
+name = "ahash"
+path = "tests/bench.rs"
+harness = false
+
+[[bench]]
+name = "map"
+path = "tests/map_tests.rs"
+harness = false
+
+[dependencies.cfg-if]
+version = "1.0"
+
+[dependencies.const-random]
+version = "0.1.17"
+optional = true
+
+[dependencies.getrandom]
+version = "0.3.1"
+optional = true
+
+[dependencies.portable-atomic]
+version = "1.0.0"
+optional = true
+
+[dependencies.serde]
+version = "1.0.117"
+optional = true
+
+[dependencies.zerocopy]
+version = "0.8.24"
+features = ["simd"]
+default-features = false
+
+[dev-dependencies.criterion]
+version = "0.3.2"
+features = ["html_reports"]
+
+[dev-dependencies.fnv]
+version = "1.0.5"
+
+[dev-dependencies.fxhash]
+version = "0.2.1"
+
+[dev-dependencies.hashbrown]
+version = "0.14.3"
+
+[dev-dependencies.hex]
+version = "0.4.2"
+
+[dev-dependencies.no-panic]
+version = "0.1.10"
+
+[dev-dependencies.pcg-mwc]
+version = "0.2.1"
+
+[dev-dependencies.rand]
+version = "0.8.5"
+
+[dev-dependencies.seahash]
+version = "4.0"
+
+[dev-dependencies.serde_json]
+version = "1.0.59"
+
+[dev-dependencies.smallvec]
+version = "1.13.1"
+
+[build-dependencies.version_check]
+version = "0.9.4"
+
+[features]
+atomic-polyfill = [
+    "dep:portable-atomic",
+    "once_cell/critical-section",
+]
+compile-time-rng = ["const-random"]
+default = [
+    "std",
+    "runtime-rng",
+]
+nightly-arm-aes = []
+no-rng = []
+runtime-rng = ["getrandom"]
+std = []
+
+[target.'cfg(not(all(target_arch = "arm", target_os = "none")))'.dependencies.once_cell]
+version = "1.18.0"
+features = ["alloc"]
+default-features = false