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/litrs-0.4.2/CHANGELOG.md

@@ -0,0 +1,111 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+
+## [Unreleased]
+
+## [0.4.2] - 2025-07-25
+- Fix incorrect byte string value with non-ASCII `\xHH` byte string escapes
+    - `ByteStringLit::parse(r#"b"\xff""#).unwrap().value()` would return `[0xc3, 0xbf]` instead of `[0xff]`.
+- Remove CR LF normalization to align with spec
+    - This is technically a breaking change, but released with a minor version bump as it just aligns with the specification. It is extremely unlikely to affect any real world use case.
+- Fix incorrect error span for out-of-range Unicode escapes
+
+## [0.4.1] - 2023-10-18
+- Fixed incorrectly labeling `27f32` a float literals in docs.
+- Added hint to integer literal docs about parsing as `u128`.
+
+## [0.4.0] - 2023-03-05
+### Added
+- Add ability to parse literals with arbitrary suffixes (e.g. `"foo"bla` or `23px`)
+- Add `suffix()` method to all literal types except `BoolLit`
+- Add `IntegerBase::value`
+- Add `from_suffix` and `suffix` methods to `FloatType` and `IntegerType`
+- Add `FromStr` and `Display` impls to `FloatType` and `IntegerType`
+
+### Changed
+- **Breaking**: Mark `FloatType` and `IntegerType` as `#[non_exhaustive]`
+- **Breaking**: Fix integer parsing for cases like `27f32`. `Literal::parse`
+  and `IntegerLit::parse` will both identify this as an integer literal.
+- **Breaking**: Fix float parsing by correctly rejecting inputs like `27f32`. A
+  float literal must have a period OR an exponent part, according to the spec.
+  Previously decimal integers were accepted in `FloatLit::parse`.
+- Improved some parts of the docs
+
+### Removed
+- **Breaking**: Remove `OwnedLiteral` and `SharedLiteral`
+
+## [0.3.0] - 2022-12-19
+### Breaking
+- Bump MSRV (minimal supported Rust version) to 1.54
+
+### Added
+- Add `raw_input` and `into_raw_input` to non-bool `*Lit` types
+- Add `impl From<*Lit> for pm::Literal` (for non-bool literals)
+- Add `impl From<BoolLit> for pm::Ident`
+
+### Fixed
+- Fix link to reference and clarify bool literals ([#7](https://github.com/LukasKalbertodt/litrs/pull/7))
+
+### Internals
+- Move lots of parsing code into non-generic functions (this hopefully reduces compile times)
+- To implement `[into_]raw_input` for integer and float literals, their
+  internals were changed a bit so that they store the full input string now.
+
+## [0.2.3] - 2021-06-09
+### Changed
+- Minor internal code change to bring MSRV from 1.52 to 1.42
+
+## [0.2.2] - 2021-06-09
+### Changed
+- Fixed (byte) string literal parsing by:
+    - Correctly handling "string continue" sequences
+    - Correctly converting `\n\r` into `\n`
+
+## [0.2.1] - 2021-06-04
+### Changed
+- Fixed the `expected` value of the error returned from `TryFrom<TokenTree>` impls in some cases
+
+## [0.2.0] - 2021-05-28
+### Changed
+- **Breaking**: rename `Error` to `ParseError`. That describes its purpose more
+    closely and is particular useful now that other error types exist in the library.
+
+### Removed
+- **Breaking**: remove `proc-macro` feature and instead offer the corresponding
+    `impl`s unconditionally. Since the feature didn't enable/disable a
+    dependency (`proc-macro` is a compiler provided crate) and since apparently
+    it works fine in `no_std` environments, I dropped this feature. I don't
+    currently see a reason why the corresponding impls should be conditional.
+
+### Added
+- `TryFrom<TokenTree> for litrs::Literal` impls
+- `From<*Lit> for litrs::Literal` impls
+- `TryFrom<proc_macro[2]::Literal> for *Lit`
+- `TryFrom<TokenTree> for *Lit`
+- `InvalidToken` error type for all new `TryFrom` impls
+
+
+## [0.1.1] - 2021-05-25
+### Added
+- `From` impls to create a `Literal` from references to proc-macro literal types:
+    - `From<&proc_macro::Literal>`
+    - `From<&proc_macro2::Literal>`
+- Better examples in README and repository
+
+## 0.1.0 - 2021-05-24
+### Added
+- Everything
+
+
+[Unreleased]: https://github.com/LukasKalbertodt/litrs/compare/v0.4.2...HEAD
+[0.4.2]: https://github.com/LukasKalbertodt/litrs/compare/v0.4.1...v0.4.2
+[0.4.1]: https://github.com/LukasKalbertodt/litrs/compare/v0.4.0...v0.4.1
+[0.4.0]: https://github.com/LukasKalbertodt/litrs/compare/v0.3.0...v0.4.0
+[0.3.0]: https://github.com/LukasKalbertodt/litrs/compare/v0.2.3...v0.3.0
+[0.2.3]: https://github.com/LukasKalbertodt/litrs/compare/v0.2.2...v0.2.3
+[0.2.2]: https://github.com/LukasKalbertodt/litrs/compare/v0.2.1...v0.2.2
+[0.2.1]: https://github.com/LukasKalbertodt/litrs/compare/v0.2.0...v0.2.1
+[0.2.0]: https://github.com/LukasKalbertodt/litrs/compare/v0.1.1...v0.2.0
+[0.1.1]: https://github.com/LukasKalbertodt/litrs/compare/v0.1.0...v0.1.1