Turn the LED exercises into the ArduinoPatterns library

[devkyato]

Summary

• replace the six blocking standalone sketches with the reusable ArduinoPatterns library while preserving their history
• add LedBank, LedAnimator, and PeriodicOutput with rollover-safe, non-blocking timing
• provide six Arduino IDE examples and PlatformIO metadata
• add native behavior tests and compile targets for Uno, ESP32, and Raspberry Pi Pico
• add API, contributor, security, issue, CI, and deterministic release packaging infrastructure

Local verification

• pio test -e native — 1 test suite / 1 reported test case passed
• pio run -e uno -e esp32dev -e pico — all 3 environments compiled
• python tools/build_release.py — generated and inspected ArduinoPatterns-1.0.0.zip

Hardware

Not hardware-tested yet. Compile compatibility is verified; follow-up hardware validation will be tracked separately.