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/basic-toml/Cargo.toml

@@ -0,0 +1,117 @@
+# 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 = "basic-toml"
+version = "0.1.10"
+authors = [
+    "Alex Crichton <alex@alexcrichton.com>",
+    "David Tolnay <dtolnay@gmail.com>",
+]
+build = false
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "Minimal TOML library with few dependencies"
+documentation = "https://docs.rs/basic-toml"
+readme = "README.md"
+keywords = [
+    "toml",
+    "serde",
+]
+categories = [
+    "config",
+    "encoding",
+    "parser-implementations",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/dtolnay/basic-toml"
+
+[package.metadata.docs.rs]
+rustdoc-args = [
+    "--generate-link-to-definition",
+    "--extern-html-root-url=core=https://doc.rust-lang.org",
+    "--extern-html-root-url=alloc=https://doc.rust-lang.org",
+    "--extern-html-root-url=std=https://doc.rust-lang.org",
+]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[lib]
+name = "basic_toml"
+path = "src/lib.rs"
+
+[[example]]
+name = "decode"
+path = "examples/decode.rs"
+
+[[test]]
+name = "datetime"
+path = "tests/datetime.rs"
+
+[[test]]
+name = "de-errors"
+path = "tests/de-errors.rs"
+
+[[test]]
+name = "display-tricky"
+path = "tests/display-tricky.rs"
+
+[[test]]
+name = "enum_external_deserialize"
+path = "tests/enum_external_deserialize.rs"
+
+[[test]]
+name = "float"
+path = "tests/float.rs"
+
+[[test]]
+name = "formatting"
+path = "tests/formatting.rs"
+
+[[test]]
+name = "invalid"
+path = "tests/invalid.rs"
+
+[[test]]
+name = "invalid-misc"
+path = "tests/invalid-misc.rs"
+
+[[test]]
+name = "parser"
+path = "tests/parser.rs"
+
+[[test]]
+name = "tokens"
+path = "tests/tokens.rs"
+
+[[test]]
+name = "valid"
+path = "tests/valid.rs"
+
+[dependencies.serde]
+version = "1.0.194"
+
+[dev-dependencies.semver]
+version = "1.0.17"
+features = ["serde"]
+
+[dev-dependencies.serde]
+version = "1.0.194"
+features = ["derive"]
+
+[dev-dependencies.serde_derive]
+version = "1.0.194"
+
+[dev-dependencies.serde_json]
+version = "1.0.99"