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/rustversion/tests/ui/bad-bound.rs

@@ -0,0 +1,7 @@
+#[rustversion::since(stable)]
+struct S;
+
+#[rustversion::any(since(stable))]
+struct S;
+
+fn main() {}

vendor/rustversion/tests/ui/bad-bound.stderr

@@ -0,0 +1,11 @@
+error: expected rustc release number like 1.85, or nightly date like 2025-02-25
+ --> tests/ui/bad-bound.rs:1:22
+  |
+1 | #[rustversion::since(stable)]
+  |                      ^^^^^^
+
+error: expected rustc release number like 1.85, or nightly date like 2025-02-25
+ --> tests/ui/bad-bound.rs:4:26
+  |
+4 | #[rustversion::any(since(stable))]
+  |                          ^^^^^^

vendor/rustversion/tests/ui/bad-date.rs

@@ -0,0 +1,7 @@
+#[rustversion::nightly(stable)]
+struct S;
+
+#[rustversion::any(nightly(stable))]
+struct S;
+
+fn main() {}

vendor/rustversion/tests/ui/bad-date.stderr

@@ -0,0 +1,11 @@
+error: expected nightly date, like 2025-02-25
+ --> tests/ui/bad-date.rs:1:24
+  |
+1 | #[rustversion::nightly(stable)]
+  |                        ^^^^^^
+
+error: expected nightly date, like 2025-02-25
+ --> tests/ui/bad-date.rs:4:28
+  |
+4 | #[rustversion::any(nightly(stable))]
+  |                            ^^^^^^

vendor/rustversion/tests/ui/bad-not.rs

@@ -0,0 +1,7 @@
+#[rustversion::any(not)]
+struct S;
+
+#[rustversion::any(not, not)]
+struct S;
+
+fn main() {}

vendor/rustversion/tests/ui/bad-not.stderr

@@ -0,0 +1,11 @@
+error: expected `(` after `not`
+ --> tests/ui/bad-not.rs:1:20
+  |
+1 | #[rustversion::any(not)]
+  |                    ^^^
+
+error: expected `(`
+ --> tests/ui/bad-not.rs:4:23
+  |
+4 | #[rustversion::any(not, not)]
+  |                       ^

vendor/rustversion/tests/ui/bad-version.rs

@@ -0,0 +1,7 @@
+#[rustversion::stable(nightly)]
+struct S;
+
+#[rustversion::any(stable(nightly))]
+struct S;
+
+fn main() {}

vendor/rustversion/tests/ui/bad-version.stderr

@@ -0,0 +1,11 @@
+error: expected rustc release number, like 1.31
+ --> tests/ui/bad-version.rs:1:23
+  |
+1 | #[rustversion::stable(nightly)]
+  |                       ^^^^^^^
+
+error: expected rustc release number, like 1.31
+ --> tests/ui/bad-version.rs:4:27
+  |
+4 | #[rustversion::any(stable(nightly))]
+  |                           ^^^^^^^

vendor/rustversion/tests/ui/const-not-fn.rs

@@ -0,0 +1,4 @@
+#[rustversion::attr(all(), const)]
+pub struct S;
+
+fn main() {}

vendor/rustversion/tests/ui/const-not-fn.stderr

@@ -0,0 +1,5 @@
+error: only allowed on a fn item
+ --> tests/ui/const-not-fn.rs:1:28
+  |
+1 | #[rustversion::attr(all(), const)]
+  |                            ^^^^^