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-config/README.md

@@ -0,0 +1,65 @@
+# esp-config
+
+[![Crates.io](https://img.shields.io/crates/v/esp-config?labelColor=1C2C2E&color=C96329&logo=Rust&style=flat-square)](https://crates.io/crates/esp-config)
+[![docs.rs](https://img.shields.io/docsrs/esp-config?labelColor=1C2C2E&color=C96329&logo=rust&style=flat-square)](https://docs.rs/esp-config)
+![MSRV](https://img.shields.io/badge/MSRV-1.79-blue?labelColor=1C2C2E&style=flat-square)
+![Crates.io](https://img.shields.io/crates/l/esp-config?labelColor=1C2C2E&style=flat-square)
+[![Matrix](https://img.shields.io/matrix/esp-rs:matrix.org?label=join%20matrix&labelColor=1C2C2E&color=BEC5C9&logo=matrix&style=flat-square)](https://matrix.to/#/#esp-rs:matrix.org)
+
+## [Documentation](https://docs.rs/crate/esp-config)
+
+## Usage
+
+`esp-config` takes a prefix (usually the crate name) and a set of configuration keys and default values to produce a configuration system that supports:
+
+- Emitting rustc cfg's for boolean keys
+- Emitting environment variables for numbers
+  - Along with decimal parsing, it supports Hex, Octal and Binary with the respective `0x`, `0o` and `0b` prefixes.
+- Emitting environment variables string values
+
+### Viewing the configuration
+
+The possible configuration values are output as a markdown table in the crates `OUT_DIR` with the format `{prefix}_config_table.md`, this can then be included into the crates top level documentation. Here is an example of the output:
+
+
+| Name | Description | Default value |
+|------|-------------|---------------|
+|**ESP_HAL_PLACE_SPI_DRIVER_IN_RAM**|Places the SPI driver in RAM for better performance|false|
+
+### Setting configuration options
+
+For any available configuration option, the environment variable or cfg is _always_ set based on the default value specified in the table. Users can override this by setting environment variables locally in their shell _or_ the preferred option is to utilize cargo's [`env` section](https://doc.rust-lang.org/cargo/reference/config.html#env).
+
+It's important to note that due to a [bug in cargo](https://github.com/rust-lang/cargo/issues/10358), any modifications to the environment, local or otherwise will only get picked up on a full clean build of the project.
+
+To see the final selected configuration another table is output to the `OUT_DIR` with the format `{prefix}_selected_config.md`.
+
+### Capturing configuration values in the downstream crate
+
+For all supported data types, there are helper macros that emit `const` code for parsing the configuration values.
+
+- Numbers - `esp_config_int!(integer_type, "ENV")`
+- Strings - `esp_config_str!("ENV")`
+- Bool - `esp_config_bool!("ENV")`
+
+In addition to environment variables, for boolean types rust `cfg`'s are emitted in snake case _without_ the prefix.
+
+## Minimum Supported Rust Version (MSRV)
+
+This crate is guaranteed to compile on stable Rust 1.79 and up. It _might_
+compile with older versions but that may change in any new patch release.
+
+## License
+
+Licensed under either of:
+
+- Apache License, Version 2.0 ([LICENSE-APACHE](../LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+- MIT license ([LICENSE-MIT](../LICENSE-MIT) or http://opensource.org/licenses/MIT)
+
+at your option.
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in
+the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without
+any additional terms or conditions.