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/embedded-graphics/Cargo.toml

@@ -0,0 +1,173 @@
+# 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"
+name = "embedded-graphics"
+version = "0.8.2"
+authors = [
+    "James Waples <james@wapl.es>",
+    "Ralf Fuest <mail@rfuest.de>",
+]
+build = false
+exclude = [
+    "/.circleci/",
+    "/.github/",
+    ".gitignore",
+    "convert_1bpp.sh",
+]
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "Embedded graphics library for small hardware displays"
+documentation = "https://docs.rs/embedded-graphics"
+readme = "README.md"
+keywords = [
+    "embedded-graphics",
+    "graphics",
+    "embedded",
+]
+categories = [
+    "embedded",
+    "no-std",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/embedded-graphics/embedded-graphics"
+
+[package.metadata.docs.rs]
+all-features = true
+
+[badges.circle-ci]
+branch = "master"
+repository = "embedded-graphics/embedded-graphics"
+
+[features]
+default = []
+defmt = [
+    "dep:defmt",
+    "embedded-graphics-core/defmt",
+]
+fixed_point = [
+    "fixed",
+    "half",
+]
+nalgebra_support = ["embedded-graphics-core/nalgebra_support"]
+
+[lib]
+name = "embedded_graphics"
+path = "src/lib.rs"
+
+[[test]]
+name = "chaining"
+path = "tests/chaining.rs"
+
+[[test]]
+name = "custom_primitive"
+path = "tests/custom_primitive.rs"
+
+[[test]]
+name = "custom_primitive_style"
+path = "tests/custom_primitive_style.rs"
+
+[[test]]
+name = "font"
+path = "tests/font.rs"
+
+[[test]]
+name = "text_renderer_generic"
+path = "tests/text_renderer_generic.rs"
+
+[[bench]]
+name = "color_conversion"
+path = "benches/color_conversion.rs"
+harness = false
+
+[[bench]]
+name = "common"
+path = "benches/common.rs"
+
+[[bench]]
+name = "contains"
+path = "benches/contains.rs"
+harness = false
+
+[[bench]]
+name = "fonts"
+path = "benches/fonts.rs"
+harness = false
+
+[[bench]]
+name = "framebuffer"
+path = "benches/framebuffer.rs"
+harness = false
+
+[[bench]]
+name = "image"
+path = "benches/image.rs"
+harness = false
+
+[[bench]]
+name = "primitives"
+path = "benches/primitives.rs"
+harness = false
+
+[[bench]]
+name = "primitives_fixed_point"
+path = "benches/primitives_fixed_point.rs"
+harness = false
+required-features = ["fixed_point"]
+
+[[bench]]
+name = "raw_data_iter"
+path = "benches/raw_data_iter.rs"
+harness = false
+
+[dependencies.az]
+version = "~1.2.0"
+
+[dependencies.byteorder]
+version = "1.4.3"
+default-features = false
+
+[dependencies.defmt]
+version = "0.3.2"
+optional = true
+
+[dependencies.embedded-graphics-core]
+version = "^0.4.1"
+
+[dependencies.fixed]
+version = "~1.27.0"
+optional = true
+default-features = false
+
+[dependencies.float-cmp]
+version = "0.9.0"
+
+[dependencies.half]
+version = "~2.4.1"
+optional = true
+default-features = false
+
+[dependencies.micromath]
+version = "2.0.0"
+default-features = false
+
+[dev-dependencies.arrayvec]
+version = "0.7.2"
+default-features = false
+
+[dev-dependencies.criterion]
+version = "0.4.0"
+features = ["html_reports"]
+default-features = false