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>

docs/plans/2026-03-03-plan-redesign-design.md

@@ -0,0 +1,41 @@
+# Plan Redesign: Waterfall → Milestone-Based Development
+
+**Date**: 2026-03-03
+
+## Problem
+
+The original 9-phase sequential plan had three issues:
+
+1. **Premature abstraction** — LedController trait designed before hardware validation
+2. **Phases too large** — multi-session phases with unclear stopping points
+3. **Hardware dependencies unclear** — couldn't tell what to work on with partial hardware
+
+## Decision
+
+Restructured into milestone-based groups organized by hardware availability:
+
+| Group | Hardware Needed | Milestones |
+|-------|----------------|------------|
+| **A** | XIAO M0 + LP5562EVM + USB cable | M1 smoke test, M2 engine patterns, M3 pattern library |
+| **B** | + NTAG5Link Click board + I2C jumper | M4 EEPROM, M5 boot-from-EEPROM, M6 SRAM mailbox |
+| **C** | + Hall sensor + multimeter | M7 sleep/wake, M8 recovery, M9 power characterization |
+| **D** | All Group A-C hardware | M10 LedController trait, M11 SimplePwm |
+| **E** | Future | Custom PCB, companion app, NFC OTA |
+
+## Key Principles
+
+- **Hardware-first**: Get real LEDs blinking before designing abstractions
+- **YAGNI**: No traits, formats, or protocols until we need them
+- **Small milestones**: Each produces a flashable, testable result (~1 session)
+- **Deferred abstraction**: LedController trait moves to M10 (after M1-M9 prove the real interface)
+- **Pattern format informed by experience**: Binary format designed in M5 after M2-M3 engine programming experience
+
+## Current Status
+
+- Phase 0 (scaffold) complete
+- M1 code ready to flash (LP5562 driver integrated, main.rs has RGBW cycle test)
+- Blocked on mini-USB cable for flashing
+
+## Reference
+
+Full plan: [docs/DEVELOPMENT_PLAN.md](../DEVELOPMENT_PLAN.md)