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_msrv_is_minimal.sh

@@ -0,0 +1,72 @@
+#!/usr/bin/env bash
+#
+# Copyright 2025 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
+
+read -r -d '' PYTHON_SCRIPT <<'EOF' || true
+import sys
+import json
+
+def parse_version(v):
+    """Converts a version string to a tuple of integers."""
+    return tuple(map(int, v.split(".")))
+
+def main():
+    """
+    Checks that the package's MSRV is strictly lower than any version
+    specified in `package.metadata.build-rs`.
+    """
+    try:
+        data = json.load(sys.stdin)
+    except json.JSONDecodeError as e:
+        print(f"Error parsing JSON from cargo metadata: {e}", file=sys.stderr)
+        sys.exit(1)
+
+    # Find the zerocopy package
+    try:
+        pkg = next(p for p in data["packages"] if p["name"] == "zerocopy")
+    except StopIteration:
+        print("Error: zerocopy package not found in metadata", file=sys.stderr)
+        sys.exit(1)
+
+    msrv_str = pkg.get("rust_version")
+    if not msrv_str:
+        print("Error: rust-version not found in Cargo.toml", file=sys.stderr)
+        sys.exit(1)
+
+    try:
+        msrv = parse_version(msrv_str)
+    except ValueError:
+        print(f"Error: Invalid MSRV format: {msrv_str}", file=sys.stderr)
+        sys.exit(1)
+
+    build_rs_versions = (pkg.get("metadata") or {}).get("build-rs", {})
+
+    failed = False
+    for name, ver_str in build_rs_versions.items():
+        try:
+            ver = parse_version(ver_str)
+        except ValueError:
+            print(f"Warning: Skipping invalid version format for {name}: {ver_str}", file=sys.stderr)
+            continue
+
+        # Check that MSRV < Version (strictly lower)
+        if not (msrv < ver):
+            print(f"Error: MSRV ({msrv_str}) is not strictly lower than {name} ({ver_str})", file=sys.stderr)
+            failed = True
+
+    if failed:
+        sys.exit(1)
+
+if __name__ == "__main__":
+    main()
+EOF
+
+cargo metadata --format-version 1 --no-deps | python3 -c "$PYTHON_SCRIPT"