Add tooling + EFM8UB20 QFP48 pinout doc

Make the repo self-contained (no dependency on the parent firmware-tools/
checkout): copy in the patch/disasm/syx tools and the c2probe RP2040 C2
flash-reader/patcher firmware.

- patch_usb1_to_cv.py : byte-level USB-1->CV patch (imported by roundtrip.py)
- d8051.py             : standalone 8051 disassembler
- syx_extract.py       : SysEx extractor
- c2probe/             : RP2040 C2 flash reader + host scripts
  (c2probe.c, cdc/dump_flash/patch_c2/reflash_page/verify.py, CMake build)
- RECOVERY.md          : C2 flash recovery procedure
- EFM8UB20_PINOUT.md   : reverse-engineered QFP48 pinout + firmware pin usage
- roundtrip.py         : import local patch_usb1_to_cv (parent as fallback)
- .gitignore           : exclude c2probe/.venv, c2probe/build

Verified: stock + patched round-trips still re-assemble byte-identical.

.gitignore

@@ -2,3 +2,6 @@ __pycache__/
 *.lst
 *.sym
 *.asm.bak
+# c2probe (RP2040) build artifacts
+c2probe/.venv/
+c2probe/build/