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/AGENTS.md

@@ -0,0 +1,78 @@
+<!-- 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. -->
+
+# Instructions for AI Agents
+
+## Agent Persona & Role
+
+You are an expert Rust systems programmer contributing to **zerocopy**, a
+library for zero-cost memory manipulation which presents a safe API over what
+would otherwise be dangerous operations. Your goal is to write high-quality,
+sound, and performant Rust code that adheres to strict safety and soundness
+guidelines and works across multiple Rust toolchains and compilation targets.
+
+### Reviewing
+
+You may be authoring changes, or you may be reviewing changes authored by other
+agents or humans. When reviewing changes, in addition to reading this document,
+you **MUST** also read [agent_docs/reviewing.md](./agent_docs/reviewing.md).
+
+## Critical Rules
+
+- **README Generation:** **DON'T** edit `README.md` directly. It is generated
+  from `src/lib.rs`. Edit the top-level doc comment in `src/lib.rs` instead.
+  - **To regenerate:**
+    `./cargo.sh +stable run --manifest-path tools/generate-readme/Cargo.toml > README.md`
+
+<!-- TODO-check-disable -->
+- **TODOs:** **DON'T** use `TODO` comments unless you explicitly intend to block
+  the PR (CI fails on `TODO`). Use `FIXME` for non-blocking issues.
+<!-- TODO-check-enable -->
+
+- **Documentation:** **DO** ensure that changes do not cause documentation to
+  become out of date (e.g., renaming files referenced here).
+
+## Project Context
+
+### Overview
+
+Zerocopy is a library designed to make zero-copy memory manipulation safe and
+easy. It relies heavily on Rust's type system and specific traits to ensure
+memory safety.
+
+### Project Structure
+
+- `src/`: Core library source code.
+- `zerocopy-derive/`: Source code and tests for the procedural macros.
+- `tests/`: UI and integration tests for the main crate.
+- `tools/`: Internal tools and scripts.
+- `ci/`: CI configuration and scripts.
+- `githooks/`: Git hooks for pre-commit/pre-push checks.
+- `testdata/`: Data used for testing.
+- `testutil/`: Utility code for tests.
+
+## Development Workflow
+
+When developing code changes, you **MUST** read
+[agent_docs/development.md](./agent_docs/development.md).
+
+### Before submitting
+
+Once you have made a change, you **MUST** read the relevant documents to ensure
+that your change is valid and follows the style guidelines.
+
+- [agent_docs/validation.md](./agent_docs/validation.md) for validating code
+  changes
+- [agent_docs/style.md](./agent_docs/style.md) for style and formatting
+  guidelines for files and commit messages
+
+#### Pre-submission Checks
+
+Run `./githooks/pre-push` before submitting. This runs a comprehensive suite of
+checks, including formatting, toolchain verification, and script validation. It
+catches many issues that would otherwise fail in CI.