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/futures-util/Cargo.toml

@@ -0,0 +1,181 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+rust-version = "1.71"
+name = "futures-util"
+version = "0.3.32"
+build = false
+autolib = false
+autobins = false
+autoexamples = false
+autotests = false
+autobenches = false
+description = """
+Common utilities and extension traits for the futures-rs library.
+"""
+homepage = "https://rust-lang.github.io/futures-rs"
+readme = "README.md"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/futures-rs"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = [
+    "--cfg",
+    "docsrs",
+]
+
+[features]
+alloc = [
+    "futures-core/alloc",
+    "futures-task/alloc",
+    "slab",
+]
+async-await = []
+async-await-macro = [
+    "async-await",
+    "futures-macro",
+]
+bilock = []
+cfg-target-has-atomic = []
+channel = [
+    "std",
+    "futures-channel",
+]
+compat = [
+    "std",
+    "futures_01",
+    "libc",
+]
+default = [
+    "std",
+    "async-await",
+    "async-await-macro",
+]
+io = [
+    "std",
+    "futures-io",
+    "memchr",
+]
+io-compat = [
+    "io",
+    "compat",
+    "tokio-io",
+    "libc",
+]
+portable-atomic = ["futures-core/portable-atomic"]
+sink = ["futures-sink"]
+std = [
+    "alloc",
+    "futures-core/std",
+    "futures-task/std",
+    "slab/std",
+]
+unstable = [
+    "futures-core/unstable",
+    "futures-task/unstable",
+]
+write-all-vectored = ["io"]
+
+[lib]
+name = "futures_util"
+path = "src/lib.rs"
+
+[[bench]]
+name = "bilock"
+path = "benches/bilock.rs"
+
+[[bench]]
+name = "flatten_unordered"
+path = "benches/flatten_unordered.rs"
+
+[[bench]]
+name = "futures_unordered"
+path = "benches/futures_unordered.rs"
+
+[[bench]]
+name = "select"
+path = "benches/select.rs"
+
+[dependencies.futures-channel]
+version = "0.3.32"
+features = ["std"]
+optional = true
+default-features = false
+
+[dependencies.futures-core]
+version = "0.3.32"
+default-features = false
+
+[dependencies.futures-io]
+version = "0.3.32"
+features = ["std"]
+optional = true
+default-features = false
+
+[dependencies.futures-macro]
+version = "=0.3.32"
+optional = true
+default-features = false
+
+[dependencies.futures-sink]
+version = "0.3.32"
+optional = true
+default-features = false
+
+[dependencies.futures-task]
+version = "0.3.32"
+default-features = false
+
+[dependencies.futures_01]
+version = "0.1.25"
+optional = true
+package = "futures"
+
+[dependencies.libc]
+version = "0.2.26"
+optional = true
+
+[dependencies.memchr]
+version = "2.2"
+optional = true
+
+[dependencies.pin-project-lite]
+version = "0.2.6"
+
+[dependencies.slab]
+version = "0.4.7"
+optional = true
+default-features = false
+
+[dependencies.spin]
+version = "0.10.0"
+optional = true
+
+[dependencies.tokio-io]
+version = "0.1.9"
+optional = true
+
+[dev-dependencies.tokio]
+version = "0.1.11"
+
+[lints.rust]
+missing_debug_implementations = "warn"
+rust_2018_idioms = "warn"
+single_use_lifetimes = "warn"
+unreachable_pub = "warn"
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+priority = 0
+check-cfg = ["cfg(futures_sanitizer)"]