Adds Serilog.Sinks.File to TeamsISO.Engine and a new EngineLogging.CreateDefault() factory that writes to BOTH the existing console sink and a rolling daily file at %LOCALAPPDATA%\\TeamsISO\\Logs\\teamsiso<date>.log. The WPF host (TeamsISO.exe is a WinExe with no console attached at runtime) now uses CreateDefault so support has something to ask for when users file an issue. The Console build keeps using CreateConsole — stdout is the right surface there and shell redirection beats a competing on-disk sink.
Files roll daily, cap at 10 MB before mid-day rollover, and only the most recent 14 are retained. Disk flush interval is 250 ms so a tail -f from another tool sees lines promptly. Path is announced via the first log line on every startup.
Two unit tests gate the wiring: AllLoggers_WriteToFile (verifies both typed and named CreateLogger() reach the file) and LogsAtBelowMinimumLevel_AreSuppressed (regression guard for level filtering). 74/74 unit tests pass (was 72).
Also adds a startup breadcrumb log line in App.OnStartup carrying the build version + PID so we can correlate a user's log file with a specific commit.
