feat: Implement initial application structure with network view and SVG editor

- Added network-view.js for visualizing network topology with devices and connections.
- Introduced svg-editor.js for managing ports on device types with drag-and-drop functionality.
- Created bootstrap.php for application initialization, including configuration and database connection.
- Established config.php for centralized configuration settings.
- Developed index.php as the main entry point with module-based routing.
- Integrated _sql.php for database abstraction.
- Added auth.php for single-user authentication handling.
- Included helpers.php for utility functions.
- Created modules for managing connections, device types, devices, and floors.
- Implemented database schema in init.sql for locations, buildings, floors, rooms, network outlets, devices, and connections.
- Added Docker support with docker-compose.yml for web and database services.
- Documented database structure and UI/UX concepts in respective markdown files.

app/.htaccess

@@ -0,0 +1,48 @@
+# =========================
+# Grundschutz
+# =========================
+
+# Kein Directory-Listing
+Options -Indexes
+
+# Schutz für sensible Dateien
+<FilesMatch "(\.env|\.git|config\.php|_sql\.php)">
+    Require all denied
+</FilesMatch>
+
+# TODO: ggf. weitere Dateien schützen, z.B. uploads oder tmp
+
+# =========================
+# Rewrite zu index.php
+# =========================
+RewriteEngine On
+
+# Alles auf index.php umleiten, außer echte Dateien/Verzeichnisse
+RewriteCond %{REQUEST_FILENAME} !-f
+RewriteCond %{REQUEST_FILENAME} !-d
+RewriteRule ^(.*)$ index.php [QSA,L]
+
+# =========================
+# Standard-Dokument
+# =========================
+DirectoryIndex index.php
+
+# =========================
+# Security Headers
+# =========================
+<IfModule mod_headers.c>
+    Header set X-Content-Type-Options "nosniff"
+    Header set X-Frame-Options "SAMEORIGIN"
+    Header set X-XSS-Protection "1; mode=block"
+    Header always set Referrer-Policy "no-referrer-when-downgrade"
+    Header always set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self'; img-src 'self' data:;"
+</IfModule>
+
+# =========================
+# Upload-Sicherheit
+# =========================
+<FilesMatch "\.(php|phtml|php3|php4|php5|php7|phps)$">
+    Require all denied
+</FilesMatch>
+
+# TODO: Optional: Upload-Verzeichnisse (device_types, floorplans) via .htaccess zusätzlich schützen