fix(i18n): clear all PyInstaller env vars (not only home dir) on relaunch (v1.13.11)

[nelsonduarte]

Summary

Shipped a regression in v1.13.10. Changing language on the Store / installer build now pops up:

`_PYI_APPLICATION_HOME_DIR environment variable is not defined!`

Root cause

PR #50 cleared `_PYI_APPLICATION_HOME_DIR` but PyInstaller `--onefile` actually uses three internal env vars to coordinate the two-phase bootloader handoff on Windows:

```
$ strings runw.exe | grep PYI
_PYI_ARCHIVE_FILE
_PYI_APPLICATION_HOME_DIR
_PYI_PARENT_PROCESS_LEVEL
```

The child process inherits `_PYI_PARENT_PROCESS_LEVEL=1` from the parent. The bootloader uses that to decide "I am a phase-2 launch, my files have already been extracted, just read `_PYI_APPLICATION_HOME_DIR` to find them". We had just cleared that path → bootloader aborts.

Fix

Replace the two explicit `env.remove("…")` calls with a pattern sweep that drops every key matching `PYI` or `_MEIPASS`. The relaunched process now truly starts as a fresh phase-1 launch and runs its own extraction, which is what we wanted from #49 / #50 in the first place.

Robust against future PyInstaller versions adding new internal vars: anything they prefix with `PYI` gets swept automatically.

Test

Built locally with the fix and ran two empirical checks:

1. Normal launch — `dist/PDFApps.exe` starts cleanly, no error dialog.
2. Relaunch simulation — spawn parent, spawn child via QProcess with sanitised env, kill parent, observe child survives. Child stayed alive after parent's atexit cleanup; no "_PYI_APPLICATION_HOME_DIR not defined" dialog.

Test plan post-merge

• Re-build via CI, tag `v1.13.11`
• Test language change 3-4 times on the new MSIX before re-submitting to the Store
• Re-submit MSIX to Partner Center, cancelling the current v1.13.10 sit-on-the-store moment is unnecessary — this fix can ship as a normal update over v1.13.10

🤖 Generated with Claude Code