ver. 0.300: Manifest-based update system with checksum verification and file backup

Replaces the manual ZIP packaging workflow with an automated build script.
UpdateRepository now supports both manifest JSON format (new) and legacy
_sql.txt/_files.txt format (fallback), enabling a smooth transition for
existing client instances.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.updateignore

@@ -0,0 +1,41 @@
+# Dokumentacja (tylko wewnetrzna/deweloperska)
+*.md
+docs/
+CLAUDE.md
+AGENTS.md
+
+# Narzedzia deweloperskie
+.claude/
+.gitignore
+.git/
+tests/
+phpunit.xml
+phpunit.phar
+composer.json
+composer.lock
+vendor/
+test.ps1
+memory/
+
+# Infrastruktura aktualizacji (meta, nie runtime)
+updates/changelog.php
+updates/versions.php
+updates/install.php
+.updateignore
+build-update.ps1
+migrations/
+
+# Pliki konfiguracyjne klienta (wdrazane osobno)
+config.php
+.htaccess
+admin/.htaccess
+libraries/version.ini
+
+# Temp / cache / backups
+temp/
+backups/
+cache/
+cron/temp/
+
+# IDE
+.vscode/