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/embassy-time-driver/gen_tick.py

@@ -0,0 +1,81 @@
+import os
+from glob import glob
+
+abspath = os.path.abspath(__file__)
+dname = os.path.dirname(abspath)
+os.chdir(dname)
+
+ticks = []
+for i in range(10):
+    ticks.append(10**i)
+for i in range(1, 25):
+    ticks.append(2**i)
+for i in range(1, 20):
+    ticks.append(2**i * 1000)
+for i in range(1, 20):
+    ticks.append(2**i * 10000)
+for i in range(1, 10):
+    ticks.append(2**i * 1000000)
+    ticks.append(2**i * 9 // 8 * 1000000)
+    ticks.append(2**i * 3 // 2 * 1000000)
+for i in range(1, 30):
+    ticks.append(10 * i * 1_000_000)
+for i in range(15, 50):
+    ticks.append(20 * i * 1_000_000)
+
+seen = set()
+ticks = sorted([x for x in ticks if not (x in seen or seen.add(x))])
+
+# ========= Update Cargo.toml
+
+SEPARATOR_START = '# BEGIN TICKS\n'
+SEPARATOR_END = '# END TICKS\n'
+HELP = '# Generated by gen_tick.py. DO NOT EDIT.\n'
+
+feats_time = ''
+feats_driver = ''
+for freq in ticks:
+    feature = f'tick-hz-{freq:_}'
+    if freq >= 1_000_000_000:
+        freq_human = f"{freq / 1_000_000_000}GHz"
+    elif freq >= 1_000_000:
+        freq_human = f"{freq / 1_000_000}MHz"
+    elif freq >= 1_000:
+        freq_human = f"{freq / 1000}kHz"
+    else:
+        freq_human = f"{freq}Hz"
+
+    feats_time += f"## {freq_human} Tick Rate\n"
+    feats_time += f"{feature} = [\"embassy-time-driver/{feature}\"]\n"
+    feats_driver += f"## {freq_human} Tick Rate\n"
+    feats_driver += f"{feature} = []\n"
+
+with open('Cargo.toml', 'r') as f:
+    data = f.read()
+before, data = data.split(SEPARATOR_START, maxsplit=1)
+_, after = data.split(SEPARATOR_END, maxsplit=1)
+with open('Cargo.toml', 'w') as f:
+    f.write(before + SEPARATOR_START + HELP + feats_driver + SEPARATOR_END + after)
+
+with open('../embassy-time/Cargo.toml', 'r') as f:
+    data = f.read()
+before, data = data.split(SEPARATOR_START, maxsplit=1)
+_, after = data.split(SEPARATOR_END, maxsplit=1)
+with open('../embassy-time/Cargo.toml', 'w') as f:
+    f.write(before + SEPARATOR_START + HELP + feats_time + SEPARATOR_END + after)
+
+# ========= Update src/tick.rs
+
+with open('src/tick.rs', 'w') as f:
+
+    f.write('// Generated by gen_tick.py. DO NOT EDIT.\n\n')
+    for hz in ticks:
+        f.write(
+            f'#[cfg(feature = "tick-hz-{hz:_}")] pub const TICK_HZ: u64 = {hz:_};\n')
+    f.write('#[cfg(not(any(\n')
+    for hz in ticks:
+        f.write(f'feature = "tick-hz-{hz:_}",\n')
+    f.write(')))] pub const TICK_HZ: u64 = 1_000_000;')
+
+
+os.system('rustfmt src/tick.rs')