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/enum-as-inner/Cargo.toml

@@ -0,0 +1,69 @@
+# 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 = "2018"
+name = "enum-as-inner"
+version = "0.6.1"
+authors = ["Benjamin Fry <benjaminfry@me.com>"]
+build = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = """
+A proc-macro for deriving inner field accessor functions on enums.
+"""
+documentation = "https://docs.rs/enum-as-inner"
+readme = "README.md"
+license = "MIT/Apache-2.0"
+repository = "https://github.com/bluejekyll/enum-as-inner"
+
+[lib]
+name = "enum_as_inner"
+path = "src/lib.rs"
+proc-macro = true
+
+[[test]]
+name = "basic"
+path = "tests/basic.rs"
+
+[[test]]
+name = "generics"
+path = "tests/generics.rs"
+
+[[test]]
+name = "named"
+path = "tests/named.rs"
+
+[[test]]
+name = "snake_case"
+path = "tests/snake_case.rs"
+
+[[test]]
+name = "unit"
+path = "tests/unit.rs"
+
+[[test]]
+name = "unnamed"
+path = "tests/unnamed.rs"
+
+[dependencies.heck]
+version = "0.5"
+
+[dependencies.proc-macro2]
+version = "1.0"
+
+[dependencies.quote]
+version = "1.0"
+
+[dependencies.syn]
+version = "2.0"