Add LP5562 driver, M1 smoke test, and milestone-based plan

- Integrate LP5562 driver from sibling project (ntag5-samd21-lp562)
  with full doc comments restored
- Update main.rs with complete M1 test: I2C init, GPIO EN, RGBW cycle
- Rewrite DEVELOPMENT_PLAN.md from waterfall to milestone-based groups
  organized by hardware availability (Groups A-E)
- Rewrite STATUS.md with milestone checklist tracking
- Add LP5562 timing constraints and flash script docs to CLAUDE.md
- Add flash_when_ready.sh for auto-flash dev workflow
- Add brainstorm design doc for plan redesign rationale

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

flash_when_ready.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+echo "Watching for XIAO bootloader... wiggle your RST wire!"
+echo "Will flash as soon as it appears."
+while true; do
+    if lsusb | grep -qi "2886"; then
+        echo "FOUND IT! Flashing now..."
+        export PATH="$HOME/.cargo/bin:$PATH"
+        cargo hf2 --release 2>&1
+        echo "Done. Exit code: $?"
+        break
+    fi
+    sleep 0.1
+done