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/winapi-util/.github/workflows/ci.yml

@@ -0,0 +1,87 @@
+name: ci
+on:
+  pull_request:
+    branches:
+    - master
+  push:
+    branches:
+    - master
+  schedule:
+  - cron: '00 01 * * *'
+
+# The section is needed to drop write-all permissions that are granted on
+# `schedule` event. By specifying any permission explicitly all others are set
+# to none. By using the principle of least privilege the damage a compromised
+# workflow can do (because of an injection or compromised third party tool or
+# action) is restricted. Currently the worklow doesn't need any additional
+# permission except for pulling the code. Adding labels to issues, commenting
+# on pull-requests, etc. may need additional permissions:
+#
+# Syntax for this section:
+# https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#permissions
+#
+# Reference for how to assign permissions on a job-by-job basis:
+# https://docs.github.com/en/actions/using-jobs/assigning-permissions-to-jobs
+#
+# Reference for available permissions that we can enable if needed:
+# https://docs.github.com/en/actions/security-guides/automatic-token-authentication#permissions-for-the-github_token
+permissions:
+  # to fetch code (actions/checkout)
+  contents: read
+
+jobs:
+  test:
+    name: test
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+        - build: pinned
+          os: windows-latest
+          rust: 1.72.0
+        - build: stable
+          os: windows-latest
+          rust: stable
+        - build: beta
+          os: windows-latest
+          rust: beta
+        - build: nightly
+          os: windows-latest
+          rust: nightly
+        - build: win-gnu
+          os: windows-latest
+          rust: stable-x86_64-gnu
+        - build: linux
+          os: ubuntu-latest
+          rust: stable
+        - build: macos
+          os: macos-latest
+          rust: stable
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+    - name: Install Rust
+      uses: dtolnay/rust-toolchain@master
+      with:
+        toolchain: ${{ matrix.rust }}
+    - run: cargo build --verbose
+    - run: cargo doc --verbose
+    - run: cargo test --verbose
+    - name: Show all computer names
+      run: cargo test --lib sysinfo::tests::itworks -- --nocapture
+
+  rustfmt:
+    name: rustfmt
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+    - name: Install Rust
+      uses: dtolnay/rust-toolchain@master
+      with:
+        toolchain: stable
+        components: rustfmt
+    - name: Check formatting
+      run: |
+        cargo fmt --all -- --check