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/esp-backtrace/Cargo.toml

@@ -0,0 +1,90 @@
+# 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 = "1.76.0"
+name = "esp-backtrace"
+version = "0.14.2"
+build = "build.rs"
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "Bare-metal backtrace support for Espressif devices"
+readme = "README.md"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/esp-rs/esp-hal"
+
+[package.metadata.docs.rs]
+default-target = "riscv32imc-unknown-none-elf"
+features = [
+    "esp32c3",
+    "panic-handler",
+    "exception-handler",
+    "println",
+    "esp-println/uart",
+]
+
+[lib]
+name = "esp_backtrace"
+path = "src/lib.rs"
+
+[dependencies.defmt]
+version = "0.3.8"
+optional = true
+
+[dependencies.esp-println]
+version = "0.12.0"
+optional = true
+default-features = false
+
+[dependencies.semihosting]
+version = "0.1.15"
+optional = true
+
+[build-dependencies.esp-build]
+version = "0.1.0"
+
+[features]
+colors = []
+custom-halt = []
+custom-pre-backtrace = []
+default = ["colors"]
+defmt = ["dep:defmt"]
+esp32 = [
+    "esp-println?/esp32",
+    "semihosting?/openocd-semihosting",
+    "print-float-registers",
+]
+esp32c2 = ["esp-println?/esp32c2"]
+esp32c3 = ["esp-println?/esp32c3"]
+esp32c6 = ["esp-println?/esp32c6"]
+esp32h2 = ["esp-println?/esp32h2"]
+esp32p4 = ["esp-println?/esp32p4"]
+esp32s2 = [
+    "esp-println?/esp32s2",
+    "semihosting?/openocd-semihosting",
+]
+esp32s3 = [
+    "esp-println?/esp32s3",
+    "semihosting?/openocd-semihosting",
+    "print-float-registers",
+]
+exception-handler = []
+halt-cores = []
+panic-handler = []
+print-float-registers = []
+println = ["dep:esp-println"]
+
+[lints.rust]
+unexpected_cfgs = "allow"