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>

Cargo.lock

@@ -28,9 +28,9 @@ checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
 
 [[package]]
 name = "az"
-version = "1.3.0"
+version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "be5eb007b7cacc6c660343e96f650fedf4b5a77512399eb952ca6642cf8d13f7"
+checksum = "7b7e4c2464d97fe331d41de9d5db0def0a96f4d823b8b32a2efd503578988973"
 
 [[package]]
 name = "bare-metal"
@@ -86,6 +86,12 @@ version = "2.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "843867be96c8daad0d758b57df9392b6d8d271134fce549de6ce169ff98a92af"
 
+[[package]]
+name = "byte-slice-cast"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7575182f7272186991736b70173b0ea045398f984bf5ebbb3804736ce1330c9d"
+
 [[package]]
 name = "bytemuck"
 version = "1.25.0"
@@ -287,6 +293,35 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "display-interface"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ba2aab1ef3793e6f7804162debb5ac5edb93b3d650fbcc5aeb72fcd0e6c03a0"
+
+[[package]]
+name = "display-interface-i2c"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d964fa85bbbb5a6ecd06e58699407ac5dc3e3ad72dac0ab7e6b0d00a1cd262d"
+dependencies = [
+ "display-interface",
+ "embedded-hal 1.0.0",
+ "embedded-hal-async",
+]
+
+[[package]]
+name = "display-interface-spi"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f86b9ec30048b1955da2038fcc3c017f419ab21bb0001879d16c0a3749dc6b7a"
+dependencies = [
+ "byte-slice-cast",
+ "display-interface",
+ "embedded-hal 1.0.0",
+ "embedded-hal-async",
+]
+
 [[package]]
 name = "document-features"
 version = "0.2.12"
@@ -535,6 +570,29 @@ dependencies = [
  "nb 1.1.0",
 ]
 
+[[package]]
+name = "embedded-graphics"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e8da660bb0c829b34a56a965490597f82a55e767b91f9543be80ce8ccb416fe"
+dependencies = [
+ "az",
+ "byteorder",
+ "embedded-graphics-core",
+ "float-cmp",
+ "micromath",
+]
+
+[[package]]
+name = "embedded-graphics-core"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "95743bef3ff70fcba3930246c4e6872882bbea0dcc6da2ca860112e0cd4bd09f"
+dependencies = [
+ "az",
+ "byteorder",
+]
+
 [[package]]
 name = "embedded-hal"
 version = "0.2.7"
@@ -823,9 +881,9 @@ dependencies = [
 
 [[package]]
 name = "fixed"
-version = "1.31.0"
+version = "1.29.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9af2cbf772fa6d1c11358f92ef554cb6b386201210bcf0e91fb7fba8a907fb40"
+checksum = "707070ccf8c4173548210893a0186e29c266901b71ed20cd9e2ca0193dfe95c3"
 dependencies = [
  "az",
  "bytemuck",
@@ -833,6 +891,15 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "float-cmp"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "98de4bbd547a563b716d8dfa9aad1cb19bfab00f4fa09a6a4ed21dbcf44ce9c4"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -991,10 +1058,12 @@ dependencies = [
  "defmt 0.3.100",
  "embassy-embedded-hal",
  "embassy-executor",
+ "embassy-futures",
  "embassy-nrf",
  "embassy-sync 0.6.2",
  "embassy-time",
  "embassy-usb",
+ "embedded-graphics",
  "esp-backtrace",
  "esp-hal",
  "esp-hal-embassy",
@@ -1006,6 +1075,7 @@ dependencies = [
  "panic-probe",
  "postcard",
  "serde",
+ "ssd1306",
  "static_cell",
 ]
 
@@ -1028,6 +1098,19 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "maybe-async-cfg"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1e083394889336bc66a4eaf1011ffbfa74893e910f902a9f271fa624c61e1b2"
+dependencies = [
+ "proc-macro-error",
+ "proc-macro2",
+ "pulldown-cmark",
+ "quote",
+ "syn 1.0.109",
+]
+
 [[package]]
 name = "memchr"
 version = "2.8.0"
@@ -1040,6 +1123,12 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "38d1115007560874e373613744c6fba374c17688327a71c1476d1a5954cc857b"
 
+[[package]]
+name = "micromath"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3c8dda44ff03a2f238717214da50f65d5a53b45cd213a7370424ffdb6fae815"
+
 [[package]]
 name = "minijinja"
 version = "2.18.0"
@@ -1280,6 +1369,30 @@ dependencies = [
  "toml_edit 0.25.8+spec-1.1.0",
 ]
 
+[[package]]
+name = "proc-macro-error"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
+dependencies = [
+ "proc-macro-error-attr",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro-error-attr"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "version_check",
+]
+
 [[package]]
 name = "proc-macro-error-attr2"
 version = "2.0.0"
@@ -1311,6 +1424,17 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "pulldown-cmark"
+version = "0.11.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "679341d22c78c6c649893cbd6c3278dcbe9fc4faa62fea3a9296ae2b50c14625"
+dependencies = [
+ "bitflags 2.11.0",
+ "memchr",
+ "unicase",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.45"
@@ -1469,6 +1593,21 @@ dependencies = [
  "lock_api",
 ]
 
+[[package]]
+name = "ssd1306"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ea6aac2d078bbc71d9b8ac3f657335311f3b6625e9a1a96ccc29f5abfa77c56"
+dependencies = [
+ "display-interface",
+ "display-interface-i2c",
+ "display-interface-spi",
+ "embedded-graphics-core",
+ "embedded-hal 1.0.0",
+ "embedded-hal-async",
+ "maybe-async-cfg",
+]
+
 [[package]]
 name = "ssmarshal"
 version = "1.0.0"
@@ -1656,6 +1795,12 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e87a2ed6b42ec5e28cc3b94c09982969e9227600b2e3dcbc1db927a84c06bd69"
 
+[[package]]
+name = "unicase"
+version = "2.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbc4bc3a9f746d862c45cb89d705aa10f187bb96c76001afab07a0d35ce60142"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.24"