fix(export): split exe path from embedded arguments to prevent double-quoting

[hikaps]

Summary

Fixes #35 — when a Playnite File action stores the full command line in the Path field (e.g. "C:\Game\game.exe" -arg1 -arg2), the exe and arguments end up bundled in SteamShortcut.Exe. The VDF quoting logic in ToObject then wraps the entire string again, producing double-quoted output like ""C:\Game\game.exe" -arg1 -arg2" which Steam cannot parse.

Root cause

The alreadyQuoted check in ToObject only handled fully-quoted strings (starts AND ends with "). A partially-quoted string like "C:\Game\game.exe" -args passes through and gets wrapped: ""C:\Game\game.exe" -args".

Changes

Three layers of defense:

1. Utils.SplitExeAndArgs(string) — new helper that detects when a command line has a quoted exe portion followed by arguments, and splits them apart.

2. CreateOrUpdateShortcut + WriteBackHandler — split exe/args before setting sc.Exe; combine split args with action.Arguments for sc.LaunchOptions. Also fixes appId generation to use the clean exe path.

3. ToObject() defense-in-depth — even if a partially-quoted exe slips through, extract only the quoted portion instead of re-wrapping the entire string.

Tests

• SplitExeAndArgs: 7 unit tests covering quoted+args, quoted-only, unquoted, unmatched quotes, whitespace, empty input
• ToObject: 6 regression tests covering the exact double-quoting scenario, already-quoted, unquoted, unmatched quote, empty/whitespace
• All existing tests should pass (CI will confirm — can't build WPF+net462 on Linux)

Files

File	Change
src/SteamShortcutsImporter/Utils.cs	+28 new SplitExeAndArgs
src/SteamShortcutsImporter/ImportExportService.cs	+12/-5 split exe/args in export
src/SteamShortcutsImporter/WriteBackHandler.cs	+8/-3 split exe/args in write-back
src/SteamShortcutsImporter/ShortcutsFile.cs	+18/-3 defense-in-depth + internal → internal
tests/ShortcutsTests/UtilsTests.cs	+67 SplitExeAndArgs tests
tests/ShortcutsTests/ShortcutsFileTests.cs	new: +67 ToObject regression tests