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/enumset_derive/Cargo.toml

@@ -0,0 +1,53 @@
+# 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 = "enumset_derive"
+version = "0.14.0"
+authors = ["Alissa Rao <aura@aura.moe>"]
+build = false
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "An internal helper crate for enumset. Not public API."
+documentation = "https://docs.rs/enumset_derive/latest/enumset_derive/"
+readme = "README.md"
+license = "MIT/Apache-2.0"
+repository = "https://github.com/Lymia/enumset"
+
+[features]
+serde2_deprecation_warning = []
+std_deprecation_warning = []
+
+[lib]
+name = "enumset_derive"
+path = "src/lib.rs"
+proc-macro = true
+
+[dependencies.darling]
+version = "0.21"
+default-features = false
+
+[dependencies.proc-macro-crate]
+version = "3"
+optional = true
+
+[dependencies.proc-macro2]
+version = "1"
+
+[dependencies.quote]
+version = "1"
+
+[dependencies.syn]
+version = "2"