initial release — panicdump v1

- Fault capture: HardFault/MemManage/BusFault/UsageFault via assembly stubs
- 192-byte fixed binary format, CRC-32 protected, magic-last atomicity
- Retained RAM (.noinit) backend, survives warm reset
- UART hex-framed export
- Python offline decoder with CFSR bit decoding and JSON output
- Mock dump generator — testable without hardware
- 50 host tests, CI via GitHub Actions