Sync working tree before initial Gitea push

- File reorg: popup/options/bulk-check moved to src/ subdirs
- Shared modules: src/shared/id-extract.js, src/options/options-shared.js
- Host updates: rcjav-host.py + register/install scripts
- .gitignore expanded

host/rcjav-host.bat

@@ -1,8 +1,12 @@
 @echo off
-REM Portable: uses Windows py launcher if present, falls back to python on PATH.
-REM Stderr redirected to log file so it can't pollute stdout (native messaging is binary).
+REM Portable: use python on PATH. Avoid py.exe as an extra native-messaging
+REM stdio hop; Chrome/Brave can be picky about inherited handles.
+REM Stderr capture lives INSIDE rcjav-host.py now (shared-access append via
+REM os.open + os.dup2). The previous `2>>` redirection here used cmd.exe's
+REM exclusive-write file handle, which caused SHARING VIOLATION races when
+REM two host processes spawned near-simultaneously — surfacing to the
+REM extension as "Error when communicating with the native messaging host."
 setlocal
 set "PYBIN=python"
-where py >nul 2>&1 && set "PYBIN=py"
 if not exist "%~dp0logs" mkdir "%~dp0logs"
-"%PYBIN%" -u "%~dp0rcjav-host.py" 2>>"%~dp0logs\rcjav-host-stderr.log"
+"%PYBIN%" -u "%~dp0rcjav-host.py"