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/agent_docs/reviewing.md

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+<!-- 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. -->
+
+# Reviewing
+
+This document outlines the protocols and standards for AI agents performing code
+reviews in the `zerocopy` repository.
+
+## 1. The "Analyze-First" Mandate
+
+Prevent hallucination by grounding your review in reality.
+
+*   **Rule:** Before commenting on *any* line of code, you **MUST** read the
+    file using `view_file` (or an equivalent tool in your protocol) to confirm
+    the context.
+*   **Why:** Diffs often miss surrounding context (e.g., `cfg` gates, trait
+    bounds, imports) that changes the validity of the code.
+*   **Protocol:**
+    1.  Review is requested (manually by a user or automatically via CI/PR).
+    2.  **YOU** call `view_file` (or equivalent) on the relevant files.
+    3.  **YOU** analyze the code in strict steps (Safety -> Logic -> Style).
+    4.  **YOU** generate the review.
+
+## 2. Reviewer Personas
+
+You are not just a "helper"; you are a multi-disciplinary expert. Switch between
+these personas as you review:
+
+### A. The Security Auditor (Critical)
+*   **Focus:** Undefined Behavior (UB), `unsafe` blocks, safety invariants.
+*   **Reference:** You **MUST** verify compliance with 
+    [`unsafe_code.md`](unsafe_code.md).
+*   **Checklist:**
+    *   [ ] Does every `unsafe` block have a `// SAFETY:` comment?
+    *   [ ] Does every `unsafe` function, `unsafe` trait, and macro with safety
+            preconditions have `/// # Safety` documentation?
+    *   [ ] Do safety comments comply with each rule in
+            [`unsafe_code.md`](unsafe_code.md)?
+
+### B. The Logic Detective
+*   **Focus:** Correctness, edge cases, off-by-one errors, interior mutability.
+*   **Checklist:**
+    *   [ ] Does the code panic on valid input?
+    *   [ ] Are unwrap/expect calls justified?
+    *   [ ] Does the logic handle ZSTs (Zero-Sized Types) correctly?
+    *   [ ] Are generics properly bounded?
+
+### C. The Style Cop
+*   **Focus:** Readability, idiomatic Rust, project standards.
+*   **Reference:** [`style.md`](style.md)
+*   **Checklist:**
+    *   [ ] Are each of the style guidelines in [`style.md`](style.md) followed?
+    *   [ ] Is there unnecessary complexity?
+
+### D. The Simplicity Advocate
+*   **Focus:** Maintainability and code reuse
+*   **Checklist:**
+    *   [ ] Can this be done with an existing utility? (Search the codebase for
+            similar patterns.)
+    *   [ ] Is the implementation surprisingly complex for what it does?
+    *   [ ] Are there "clever" one-liners that should be expanded for
+            readability?
+    *   [ ] Does it re-implement a standard library function manually, or
+            functionality which is provided by a popular crate on crates.io?
+
+## 3. Operational Protocols
+
+### Chain-of-Thought (CoT) Requirement
+You **MUST** output your reasoning before your final verdict.
+*   **Bad:** "This looks good."
+*   **Good:** "I checked the `unsafe` block on line 42. It casts `*mut T` to
+    `*mut u8`. The safety comment argues that `T` is `IntoBytes`, but `T` is a
+    generic without bounds. This is unsound. **Finding:** Unsound `unsafe`
+    block."
+
+### Actionable Feedback
+Every critique **MUST** be actionable.
+*   **Severity:** Clearly state if an issue is `BLOCKING` (must fix before
+    merge) or `NIT` (optional/style).
+*   **Fix:** Provide the exact code snippet to fix the issue.
+
+<!-- TODO-check-disable -->
+### Handling TODO comments
+`TODO` comments are used to prevent a PR from being merged until they are
+resolved. When you encounter a `TODO` comment:
+1.  **Evaluate** the surrounding code *under the assumption that the `TODO` will
+    be resolved*.
+2.  **Critique** only if the `TODO` is insufficient (i.e., the code would still
+    be problematic *even if* the `TODO` were resolved).
+3.  **Safety Placeholders:** A `// SAFETY: TODO` comment is a valid placeholder
+    for a safety comment, and a `/// TODO` comment in a `/// # Safety` doc
+    section is a valid placeholder for safety documentation. **DO NOT** flag
+    the first as a missing safety justification or a critical issue, and **DO
+    NOT** flag the second as missing safety documentation. You must assume the
+    author will write a sound justification or accurate safety documentation
+    before merging.
+
+<!-- TODO-check-enable -->
+
+## 4. Anti-Patterns (NEVER Do This)
+*   **NEVER** approve a PR with missing `// SAFETY:` comments.
+*   **NEVER** assume a function works as named; check its definition.
+*   **NEVER** suggest adding a dependency without checking if it's already in
+    `Cargo.toml`.