refactor: vendor iOpenPod core modules instead of pip dependency

Vendored 5 packages from iOpenPod (TheRealSavi/iOpenPod):
  iTunesDB_Writer/  — binary iTunesDB generation
  iTunesDB_Shared/  — field defs, constants, album identity
  SQLiteDB_Writer/  — SQLite databases for Nano 6G/7G
  iTunesDB_Parser/  — play stats reading from iPod
  ipod_device/      — device detection, FireWire ID, capabilities

Rationale: iOpenPod is a standalone iPod manager app, not a library.
Pulling it as a pip dependency is heavy and confusing for users.

Changes:
  + src/vendor/   — 77 .py files + calcHashAB.wasm (506 KB)
  ~ ipod_nano7_db.py  — _find_iop_root() now returns src/vendor/
  ~ requirements.txt   — iopenpod replaced with wasmtime + pycryptodome
  ~ .gitignore         — removed iOpenPod/ exclusion
  (setup.py reads requirements.txt automatically)

.gitignore

@@ -37,4 +37,3 @@ converted/
 specs.md
 *.AppImage
 squashfs-root/
-iOpenPod/