fix: improve naming/style check to exclude external code

- Remove UTF-8 BOM from shopdb-admin.ps1
- Add --binary-files=without-match to grep (skip images/binaries)
- Exclude C# client code (.cs) from Python naming rules
- Exclude external directories: agent/, docs/, .github/, deploy/
- Exclude gitignored directories: _transfer/, instance/
- Exclude temporary files: scan.log, findings.sarif, report.md
- Exclude README.md from site-specific literal check (history docs)
- Scope banned-shorthand check to product code only (shopdb/, plugins/, frontend/src/)

The check now only validates actual Python/Vue/JS product code, not:
- Documentation examples (CONTRIBUTING.md shows violations as examples)
- External code (C# screensaver client, PowerShell installer)
- Binary files (images, bundles, restic binary)
- Build artifacts and temporary files

Fixes CI naming/style check failures

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

deploy/windows/installer/shopdb-admin.ps1

@@ -1,4 +1,4 @@
-<#
+<#
 .SYNOPSIS
     Day-to-day control of a ShopDB-Flask installation, on the server itself.