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/ssd1306/Cargo.toml

@@ -0,0 +1,224 @@
+# 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 = "1.75.0"
+name = "ssd1306"
+version = "0.10.0"
+authors = ["James Waples <jamwaffles@gmail.com>"]
+build = false
+exclude = [
+    "build.rs",
+    "build.sh",
+    "memory.x",
+    "doc",
+    "*.jpg",
+    "*.png",
+    "*.bmp",
+]
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "I2C/SPI driver for the SSD1306 OLED display controller"
+documentation = "https://docs.rs/ssd1306"
+readme = "README.md"
+keywords = [
+    "no-std",
+    "ssd1306",
+    "oled",
+    "embedded",
+    "embedded-hal-driver",
+]
+categories = [
+    "embedded",
+    "no-std",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-embedded-community/ssd1306"
+resolver = "2"
+
+[package.metadata.docs.rs]
+all-features = true
+targets = [
+    "thumbv7m-none-eabi",
+    "thumbv7em-none-eabihf",
+]
+
+[features]
+async = ["dep:embedded-hal-async"]
+default = ["graphics"]
+graphics = ["embedded-graphics-core"]
+
+[lib]
+name = "ssd1306"
+path = "src/lib.rs"
+
+[[example]]
+name = "async_i2c_spi"
+path = "examples/async_i2c_spi.rs"
+required-features = ["async"]
+
+[[example]]
+name = "async_terminal_i2c"
+path = "examples/async_terminal_i2c.rs"
+required-features = ["async"]
+
+[[example]]
+name = "bmp_i2c"
+path = "examples/bmp_i2c.rs"
+
+[[example]]
+name = "graphics"
+path = "examples/graphics.rs"
+
+[[example]]
+name = "graphics_i2c"
+path = "examples/graphics_i2c.rs"
+
+[[example]]
+name = "graphics_i2c_128x32"
+path = "examples/graphics_i2c_128x32.rs"
+
+[[example]]
+name = "graphics_i2c_72x40"
+path = "examples/graphics_i2c_72x40.rs"
+
+[[example]]
+name = "image_i2c"
+path = "examples/image_i2c.rs"
+
+[[example]]
+name = "noise_i2c"
+path = "examples/noise_i2c.rs"
+
+[[example]]
+name = "pixelsquare"
+path = "examples/pixelsquare.rs"
+
+[[example]]
+name = "rotation_i2c"
+path = "examples/rotation_i2c.rs"
+
+[[example]]
+name = "rtic_brightness"
+path = "examples/rtic_brightness.rs"
+
+[[example]]
+name = "rtic_dvd"
+path = "examples/rtic_dvd.rs"
+
+[[example]]
+name = "terminal_i2c"
+path = "examples/terminal_i2c.rs"
+
+[[example]]
+name = "text_i2c"
+path = "examples/text_i2c.rs"
+
+[dependencies.display-interface]
+version = "0.5.0"
+
+[dependencies.display-interface-i2c]
+version = "0.5.0"
+
+[dependencies.display-interface-spi]
+version = "0.5.0"
+
+[dependencies.embedded-graphics-core]
+version = "0.4.0"
+optional = true
+
+[dependencies.embedded-hal]
+version = "1.0.0"
+
+[dependencies.embedded-hal-async]
+version = "1.0.0"
+optional = true
+
+[dependencies.maybe-async-cfg]
+version = "=0.2.4"
+
+[dev-dependencies.embedded-graphics]
+version = "0.8.0"
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.cortex-m]
+version = "0.7.2"
+features = ["critical-section-single-core"]
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.cortex-m-rt]
+version = "0.7.3"
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.cortex-m-rtic]
+version = "1.1.4"
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.defmt]
+version = "0.3.6"
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.defmt-rtt]
+version = "0.4.0"
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.embassy-embedded-hal]
+version = "0.3.0"
+default-features = false
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.embassy-executor]
+version = "0.7.0"
+features = [
+    "arch-cortex-m",
+    "executor-thread",
+    "defmt",
+]
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.embassy-futures]
+version = "0.1.1"
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.embassy-stm32]
+version = "0.2.0"
+features = [
+    "stm32f103c8",
+    "memory-x",
+    "defmt",
+    "exti",
+    "time-driver-tim3",
+    "unstable-pac",
+]
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.embassy-time]
+version = "0.4.0"
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.embedded-hal-bus]
+version = "0.3.0"
+features = ["async"]
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.panic-probe]
+version = "0.3.1"
+features = ["print-defmt"]
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.rand]
+version = "0.8.4"
+features = ["small_rng"]
+default-features = false
+
+[target.'cfg(target_arch="arm")'.dev-dependencies.tinybmp]
+version = "0.6.0"
+
+[profile.dev]
+opt-level = "s"
+codegen-units = 1
+incremental = false
+
+[profile.release]
+lto = true
+codegen-units = 1
+debug = 2