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/thiserror/Cargo.toml

@@ -0,0 +1,119 @@
+# 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 = "1.68"
+name = "thiserror"
+version = "2.0.18"
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+build = "build.rs"
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "derive(Error)"
+documentation = "https://docs.rs/thiserror"
+readme = "README.md"
+keywords = [
+    "error",
+    "error-handling",
+    "derive",
+]
+categories = [
+    "rust-patterns",
+    "no-std",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/dtolnay/thiserror"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+rustdoc-args = [
+    "--generate-link-to-definition",
+    "--generate-macro-expansion",
+    "--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",
+]
+
+[features]
+default = ["std"]
+std = []
+
+[lib]
+name = "thiserror"
+path = "src/lib.rs"
+
+[[test]]
+name = "compiletest"
+path = "tests/compiletest.rs"
+
+[[test]]
+name = "test_backtrace"
+path = "tests/test_backtrace.rs"
+
+[[test]]
+name = "test_display"
+path = "tests/test_display.rs"
+
+[[test]]
+name = "test_error"
+path = "tests/test_error.rs"
+
+[[test]]
+name = "test_expr"
+path = "tests/test_expr.rs"
+
+[[test]]
+name = "test_from"
+path = "tests/test_from.rs"
+
+[[test]]
+name = "test_generics"
+path = "tests/test_generics.rs"
+
+[[test]]
+name = "test_lints"
+path = "tests/test_lints.rs"
+
+[[test]]
+name = "test_option"
+path = "tests/test_option.rs"
+
+[[test]]
+name = "test_path"
+path = "tests/test_path.rs"
+
+[[test]]
+name = "test_source"
+path = "tests/test_source.rs"
+
+[[test]]
+name = "test_transparent"
+path = "tests/test_transparent.rs"
+
+[dependencies.thiserror-impl]
+version = "=2.0.18"
+
+[dev-dependencies.anyhow]
+version = "1.0.73"
+
+[dev-dependencies.ref-cast]
+version = "1.0.18"
+
+[dev-dependencies.rustversion]
+version = "1.0.13"
+
+[dev-dependencies.trybuild]
+version = "1.0.108"
+features = ["diff"]