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-synopsys-usb-otg/Cargo.toml

@@ -0,0 +1,61 @@
+# 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 = "esp-synopsys-usb-otg"
+version = "0.4.2"
+authors = [
+    "Vadim Kaushan <admin@disasm.info>",
+    "The ESP-RS Team",
+]
+build = "build.rs"
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = "'usb-device' implementation for Synopsys USB OTG IP cores"
+readme = "README.md"
+keywords = [
+    "no-std",
+    "embedded",
+    "usb",
+]
+license = "MIT"
+repository = "https://github.com/esp-rs-compat/synopsys-usb-otg"
+
+[package.metadata.docs.rs]
+features = ["fs"]
+
+[lib]
+name = "esp_synopsys_usb_otg"
+path = "src/lib.rs"
+
+[dependencies.critical-section]
+version = "1.1.1"
+
+[dependencies.embedded-hal]
+version = "0.2.4"
+
+[dependencies.ral-registers]
+version = "0.1.3"
+
+[dependencies.usb-device]
+version = "0.3"
+
+[dependencies.vcell]
+version = "0.1.0"
+
+[features]
+esp32sx = []
+fs = []
+hs = []
+xcvrdly = []