fix: address Copilot PR review comments

- Move save_init_options() before preset install so skills propagation
  works during 'specify init --preset --ai-skills'
- Clean up downloaded ZIP after successful preset install during init
- Validate --from URL scheme (require HTTPS, HTTP only for localhost)
- Expose unregister_commands() on extensions.py CommandRegistrar wrapper
  instead of reaching into private _registrar field
- Use _get_merged_packs() for search() and get_pack_info() so all
  active catalogs are searched, not just the highest-priority one
- Fix fetch_catalog() cache to verify cached URL matches current URL
- Fix PresetResolver: script resolution uses .sh extension, consistent
  file extensions throughout resolve(), and resolve_with_source()
  delegates to resolve() to honor template_type parameter
- Fix bash common.sh: fall through to directory scan when python3
  returns empty preset list
- Fix PowerShell Resolve-Template: filter out dot-folders and sort
  extensions deterministically

scripts/powershell/common.ps1

@@ -189,7 +189,7 @@ function Resolve-Template {
     # Priority 3: Extension-provided templates
     $extDir = Join-Path $RepoRoot '.specify/extensions'
     if (Test-Path $extDir) {
-        foreach ($ext in Get-ChildItem -Path $extDir -Directory -ErrorAction SilentlyContinue) {
+        foreach ($ext in Get-ChildItem -Path $extDir -Directory -ErrorAction SilentlyContinue | Where-Object { $_.Name -notlike '.*' } | Sort-Object Name) {
             $candidate = Join-Path $ext.FullName "templates/$TemplateName.md"
             if (Test-Path $candidate) { return $candidate }
         }