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/bitflags/Cargo.toml

@@ -0,0 +1,120 @@
+# 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 = "1.56.0"
+name = "bitflags"
+version = "2.11.0"
+authors = ["The Rust Project Developers"]
+build = false
+exclude = [
+    "/tests",
+    "/.github",
+]
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = """
+A macro to generate structures which behave like bitflags.
+"""
+homepage = "https://github.com/bitflags/bitflags"
+documentation = "https://docs.rs/bitflags"
+readme = "README.md"
+keywords = [
+    "bit",
+    "bitmask",
+    "bitflags",
+    "flags",
+]
+categories = ["no-std"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/bitflags/bitflags"
+
+[package.metadata.docs.rs]
+features = ["example_generated"]
+
+[features]
+example_generated = []
+serde = ["serde_core"]
+std = []
+
+[lib]
+name = "bitflags"
+path = "src/lib.rs"
+
+[[example]]
+name = "custom_bits_type"
+path = "examples/custom_bits_type.rs"
+
+[[example]]
+name = "custom_derive"
+path = "examples/custom_derive.rs"
+
+[[example]]
+name = "fmt"
+path = "examples/fmt.rs"
+
+[[example]]
+name = "macro_free"
+path = "examples/macro_free.rs"
+
+[[example]]
+name = "serde"
+path = "examples/serde.rs"
+
+[[bench]]
+name = "parse"
+path = "benches/parse.rs"
+
+[dependencies.arbitrary]
+version = "1.0"
+optional = true
+
+[dependencies.bytemuck]
+version = "1.12"
+optional = true
+
+[dependencies.serde_core]
+version = "1.0.228"
+optional = true
+default-features = false
+
+[dev-dependencies.arbitrary]
+version = "1.0"
+features = ["derive"]
+
+[dev-dependencies.bytemuck]
+version = "1.12.2"
+features = ["derive"]
+
+[dev-dependencies.rustversion]
+version = "1.0"
+
+[dev-dependencies.serde_json]
+version = "1.0"
+
+[dev-dependencies.serde_lib]
+version = "1.0.103"
+features = ["derive"]
+package = "serde"
+
+[dev-dependencies.serde_test]
+version = "1.0.19"
+
+[dev-dependencies.trybuild]
+version = "1.0.18"
+
+[dev-dependencies.zerocopy]
+version = "0.8"
+features = ["derive"]