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/windows-link/Cargo.toml

@@ -0,0 +1,39 @@
+# 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 = "1.71"
+name = "windows-link"
+version = "0.2.1"
+build = false
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "Linking for Windows"
+readme = "readme.md"
+categories = ["os::windows-apis"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/microsoft/windows-rs"
+
+[lib]
+name = "windows_link"
+path = "src/lib.rs"
+
+[lints.rust]
+missing_unsafe_on_extern = "warn"
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+priority = 0
+check-cfg = ["cfg(windows_raw_dylib, windows_slim_errors)"]