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/proc-macro-error/Cargo.toml

@@ -0,0 +1,56 @@
+# 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 believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "proc-macro-error"
+version = "1.0.4"
+authors = ["CreepySkeleton <creepy-skeleton@yandex.ru>"]
+build = "build.rs"
+description = "Almost drop-in replacement to panics in proc-macros"
+readme = "README.md"
+keywords = ["proc-macro", "error", "errors"]
+categories = ["development-tools::procedural-macro-helpers"]
+license = "MIT OR Apache-2.0"
+repository = "https://gitlab.com/CreepySkeleton/proc-macro-error"
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+[dependencies.proc-macro-error-attr]
+version = "=1.0.4"
+
+[dependencies.proc-macro2]
+version = "1"
+
+[dependencies.quote]
+version = "1"
+
+[dependencies.syn]
+version = "1"
+optional = true
+default-features = false
+[dev-dependencies.serde_derive]
+version = "=1.0.107"
+
+[dev-dependencies.toml]
+version = "=0.5.2"
+
+[dev-dependencies.trybuild]
+version = "1.0.19"
+features = ["diff"]
+[build-dependencies.version_check]
+version = "0.9"
+
+[features]
+default = ["syn-error"]
+syn-error = ["syn"]
+[badges.maintenance]
+status = "passively-maintained"