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/basic-toml/tests/valid/multiline-string.toml

@@ -0,0 +1,34 @@
+multiline_empty_one = """"""
+multiline_empty_two = """
+"""
+multiline_empty_three = """\
+    """
+multiline_empty_four = """\
+   \
+   \
+   """
+multiline_empty_five = """\
+   \ 
+   \	
+   \ 	
+   """
+
+equivalent_one = "The quick brown fox jumps over the lazy dog."
+equivalent_two = """
+The quick brown \
+
+
+  fox jumps over \
+    the lazy dog."""
+
+equivalent_three = """\
+       The quick brown \
+       fox jumps over \
+       the lazy dog.\
+       """
+
+equivalent_four = """\
+       The quick brown \ 
+       fox jumps over \				
+       the lazy dog.\	
+       """