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/zerocopy/ci/check_versions.sh

@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+#
+# Copyright 2024 The Fuchsia Authors
+#
+# Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+# <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+# license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+# This file may not be copied, modified, or distributed except according to
+# those terms.
+
+set -eo pipefail
+
+# Usage: version <crate-name>
+function version {
+  cargo metadata -q --format-version 1 | jq -r ".packages[] | select(.name == \"$1\").version"
+}
+
+ver_zerocopy=$(version zerocopy)
+ver_zerocopy_derive=$(version zerocopy-derive)
+
+# Usage: dependency-version <kind> <target>
+function dependency-version {
+  KIND="$1"
+  TARGET="$2"
+  cargo metadata -q --format-version 1 \
+    | jq -r ".packages[] | select(.name == \"zerocopy\").dependencies[] | select((.name == \"zerocopy-derive\") and .kind == $KIND and .target == $TARGET).req"
+}
+
+# The non-dev dependency version (kind `null` filters out the dev
+# dependency, and target `null` filters out the targeted version).
+zerocopy_derive_dep_ver=$(dependency-version null null)
+
+# The non-dev dependency, targeted version (kind `null` filters out
+# the dev dependency).
+zerocopy_derive_targeted_ver=$(dependency-version null '"cfg(any())"')
+
+# The dev dependency version (kind `"dev"` selects only the dev
+# dependency).
+zerocopy_derive_dev_dep_ver=$(dependency-version '"dev"' null)
+
+function assert-match {
+  VER_A="$1"
+  VER_B="$2"
+  SUCCESS_MSG="$3"
+  FAILURE_MSG="$4"
+  if [[ "$VER_A" == "$VER_B" ]]; then
+    echo "$SUCCESS_MSG" | tee -a $GITHUB_STEP_SUMMARY
+  else
+    echo "$FAILURE_MSG" | tee -a $GITHUB_STEP_SUMMARY >&2
+    exit 1
+  fi
+}
+
+assert-match "$ver_zerocopy" "$ver_zerocopy_derive" \
+  "Same crate version ($ver_zerocopy) found for zerocopy and zerocopy-derive." \
+  "Different crate versions found for zerocopy ($ver_zerocopy) and zerocopy-derive ($ver_zerocopy_derive)."
+
+# Note the leading `=` sign - the dependency needs to be an exact one.
+assert-match "=$ver_zerocopy_derive" "$zerocopy_derive_dep_ver" \
+  "zerocopy depends upon same version of zerocopy-derive in-tree ($zerocopy_derive_dep_ver)." \
+  "zerocopy depends upon different version of zerocopy-derive ($zerocopy_derive_dep_ver) than the one in-tree ($ver_zerocopy_derive)."
+
+# Note the leading `=` sign - the dependency needs to be an exact one.
+assert-match "=$ver_zerocopy_derive" "$zerocopy_derive_dev_dep_ver" \
+  "In dev mode, zerocopy depends upon same version of zerocopy-derive in-tree ($zerocopy_derive_dev_dep_ver)." \
+  "In dev mode, zerocopy depends upon different version of zerocopy-derive ($zerocopy_derive_dev_dep_ver) than the one in-tree ($ver_zerocopy_derive)."
+
+assert-match "$zerocopy_derive_dep_ver" "$zerocopy_derive_targeted_ver" \
+  "Same crate version ($zerocopy_derive_dep_ver) found for optional and targeted zerocopy-derive dependency." \
+  "Different crate versions found for optional ($zerocopy_derive_dep_ver) and targeted ($zerocopy_derive_targeted_ver) dependency."