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/embedded-graphics/RELEASES.md

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+# Releases
+
+Release notes for [embedded-graphics](https://crates.io/crates/embedded-graphics).
+
+## 0.8.1
+
+- `MonoTextStyleBuilder` methods are now `const`  
+- MSRV bumped to 1.71.1
+
+## 0.7.0
+
+### Primitives
+
+New primitives have been added:
+
+- `Arc`
+- `Sector`
+- `Polyline`
+- `Ellipse`
+- `RoundedRectangle`
+
+The `Line` and `Triangle` primitives now support stroke widths greater than 1px.
+
+Primitives now support stroke alignment using the `StrokeAlignment` enum.
+
+The outline of all closed shapes now can now be offset by using the `OffsetOutline::offset` method.
+
+The `ContainsPoint::contains` method can be used to check if a point is inside a primitive.
+
+All primitives can be converted into an iterator over the contained points by using the `PointsIter::points` method.
+
+### Geometry
+
+Adds the `Point::x_axis`, `Point::y_axis`, `Size::x_axis` and `Size::y_axis` methods to get one axis of a point or size, with the other set to zero.
+
+```rust
+use embedded_graphics::geometry::Point;
+
+let point = Point::new(15, 23);
+
+assert_eq!(point.x_axis() = Point::new(15, 0));
+assert_eq!(point.y_axis() = Point::new(0, 23));
+```
+
+`Point::new_equal` and `Size::new_equal` have also been added as convenience methods to create points or sizes with equal coordinates.
+
+```diff
+use embedded_graphics::geometry::Size;
+
+- let size = Size::new(20, 20);
++ let size = Size::new_equal(20);
+```
+
+Other methods added to both `Point` and `Size` are:
+
+- `component_min`
+- `component_max`
+- `component_mul`
+- `component_div`
+
+`Angle` was added to represent angles in `Arc` and `Sector` primitives.
+
+The `Rectangle::intersection` method was added to get the intersecting area of two rectangles.
+
+### Color
+
+New color constants for the CSS colors were added for all RGB color types. The color constants are
+defined in the `WebColors` trait, which is included in the prelude. The names of the constants are
+prefixed by `CSS_` to avoid naming conflicts with the existing color constants. The CSS color
+`hotpink` can, for example, be accessed by using `Rgb888::CSS_HOT_PINK`.
+
+The `ToBytes` trait has been added to support conversion of colors into byte arrays.
+
+All builtin color types can now be converted to any other builtin color type by using `From` or `Into`.
+
+### Draw target adapters
+
+The `DrawTargetExt` trait is introduced to allow a translated, cropped or clipped sub-area of a `DrawTarget` to be drawn to.
+
+`DrawTargetExt` is implemented for `DrawTarget`.
+
+Please search for `DrawTargetExt` at <https://docs.rs/embedded-graphics> for usage examples.
+
+### Fonts and text
+
+Support for external text renderers was added. To support this the existing `fonts` module has been
+split into one for the generic `Text` drawable and one for the builtin monospaced text renderer.
+Refer to the migration guide for more information about this change.
+
+Additional languages are supported by new fonts which are available in ASCII, multiple ISO-8859 and
+JIS X 201 glpyh subsets.
+
+`Text` drawables now support horizontal alignment, baseline and line height settings.
+
+The builtin monospaced text renderer now supports underline and strikethough decorations.
+
+```rust
+use embedded_graphics::{
+    mono_font::{ascii::FONT_8X13, MonoTextStyleBuilder},
+    pixelcolor::Rgb888,
+    prelude::*,
+    text::{Alignment, Baseline, Text, TextStyleBuilder},
+};
+
+// Use the builtin 8x13 monospace font with red foreground color
+let character_style = MonoTextStyleBuilder::new()
+    .font(&FONT_8X13)
+    .text_color(Rgb888::CSS_TOMATO)
+    .build();
+
+// Anchor the text relative to its horizontal center point and vertical middle
+let center_aligned = TextStyleBuilder::new()
+    .alignment(Alignment::Center)
+    .baseline(Baseline::Middle)
+    .build();
+
+Text::with_text_style(
+    "Center aligned text",
+    Point::new(100, 20),
+    character_style,
+    center_aligned,
+)
+.draw(&mut display)?;
+```
+
+### Images
+
+`SubImage` was added to draw a part of an image.
+
+```rust
+use embedded_graphics::{image::Image, pixelcolor::Rgb888, prelude::*, primitives::Rectangle};
+use tinytga::Tga;
+
+// Load spritemap TGA image
+let tiles: Tga<Rgb888> = Tga::from_slice(include_bytes!("assets/sprites.tga")).unwrap();
+
+// Grab a 64x64px subsection of the image
+let sprite_a = tiles.sub_image(&Rectangle::new(Point::new(0, 0), Size::new(64, 64)));
+
+// Draw the sprite with its top left corner at (25, 35)
+Image::new(&sprite_a, Point::new(25, 35)).draw(&mut display)?;
+```
+
+### Performance
+
+The performance of many drawing operations has been improved by drawing larger contiguous regions
+of pixels instead of individual pixels.
+
+### Mock display
+
+`MockDisplay` now supports all RGB and grayscale color types in its patterns.
+
+By setting the environment variable `EG_FANCY_PANIC=1` when running the tests, failing `MockDisplay` assertions can now pretty print the difference between two `MockDisplay`s.
+
+New methods:
+
+- `affected_area` - gets the bounding box of all changes made to the display.
+- `assert_eq_with_message` - the same as above, but with the ability to write custom messages in the test output.
+- `assert_eq` - check for equality against another `MockDisplay` and panic if they are not the same.
+- `assert_pattern_with_message` - the same as above, but with the ability to write custom messages in the test output.
+- `assert_pattern` - check for equality against a pattern and panic if they do not match.
+- `diff` - compare the display against another `MockDisplay`, producing a new `MockDisplay` containing the colored difference between them.
+- `from_points` - create a `MockDisplay` from an iterator over `Point`s.
+- `map` - create a copy of the current display with a predicate applied to all pixels.
+- `set_allow_out_of_bounds_drawing` - if set to `true`, disables the panicking behavior when a drawing operation attempts to draw pixels outside the visible mock display area.
+- `set_allow_overdraw` - if set to `true`, disables the panicking behavior when a pixel is drawn to twice.
+- `set_pixels` - sets the points in an iterator to the given color.
+- `swap_xy` - copies the current display with X and Y coordinates swapped.