Add LP5562EVM USB-I2C control tool, document reverse-engineered protocol

Reverse-engineered the MSP430 serial protocol on the LP5562EVM:
- I<addr><reg> reads, O<addr><reg><data> writes, status 00=OK / 02=NAK
- EN pin must be jumpered to VDD (MSP430 doesn't drive it after reset)
- CONFIG (0x0B) is write-only, W_CURRENT (0x09) not writable via bridge
- LED cycling verified: all 4 channels respond to direct PWM control

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

docs/STATUS.md

@@ -1,7 +1,7 @@
 # xblink Project Status
 
-**Current Milestone**: M1 — LED Smoke Test (code ready, needs USB cable to flash)
-**Last Updated**: 2026-03-03
+**Current Milestone**: M1 — LED Smoke Test (I2C verified via EVM USB bridge, XIAO M0 flash pending)
+**Last Updated**: 2026-03-05
 
 ---
 
@@ -23,7 +23,8 @@
 - [x] Create `src/led/mod.rs` with re-exports
 - [x] Update `main.rs` with I2C init + GPIO EN + LP5562 direct PWM test
 - [x] Verify `cargo build --release` compiles
-- [ ] Flash and verify RGBW LED channels on LP5562EVM
+- [x] Verify LP5562 I2C control via EVM USB-to-I2C bridge (`tools/lp5562_evm.py`)
+- [ ] Flash XIAO M0 and verify RGBW LED channels with Rust firmware
 
 ### M2: Engine Patterns