PHLEGM v8 - End User Package Retention - Checkpoint 76

Observed user symptom:
- End-User ZIP absent from the expected sibling directory after a build.
- A supplied 2026-1011-1242-2961 compiler log actually reports four passing
  native Windows targets, a generated/verified Full-Data ZIP, a successful
  merge/clone, and exit code 0. Therefore creation failure on that particular
  run is NOT established by those logs.

Packaging flaw addressed:
- Prior version moved the last successful archive family into build/archives
  before making and verifying the replacement package. An interrupted or
  failing subsequent package operation could leave no deliverable in the
  sibling directory, despite the last successful build.

Changes:
- Retain previous passing packages during compilation/packaging.
- Only archive older packages after the replacement ZIP and SHA-256/SHA-512
  sidecars are produced and the replacement archive has passed verification.
- Never archive the new/current ZIP or its sidecars.
- Refuse same-name/timestamp collisions instead of overwriting good packages.
- Do not fail a passing new package solely because an old artifact cannot
  be moved to archival storage; log a warning and retain the new package.
- Verify published ZIP and checksums are still present at the end of build,
  AFTER the optional non-destructive clone; log the exact confirmed full path.
- Added tests/EndUser-Archive-Retention.Tests.ps1 which parses the native
  PowerShell builder and checks retention / archival handling without invoking
  FreeBASIC. Execute on Windows with Windows PowerShell 5.1 as follows:
  powershell.exe -NoProfile -ExecutionPolicy Bypass -File
      ./tests/EndUser-Archive-Retention.Tests.ps1

Unchanged:
- Native Windows 32/64 OpenGL/D3D11 and Linux target matrices.
- Clone path ../../<project> v<version>/; no cfg/cfg nesting.
- Bootstrap scripts and the icon renderer (icon appearance remains a
  separate known issue).

Validation for this checkpoint:
- Source/syntax ordering checked statically.
- ZIP CRC/integrity, and SHA-256/SHA-512 sidecars verified when packaged.
- Cannot execute native FreeBASIC/Windows PowerShell in this environment;
  hands-on End-User creation and UI output still need a real Windows run.
