refactor: rename database → storage

More semantically accurate: contains SQLite files, schema, fixtures, test data.
Updated all references in code, scripts, docs.

docs/MIGRATION_COMPLETE.md

@@ -66,7 +66,7 @@ posterg-website/
 
 **Before:**
 - ❌ All files in DocumentRoot (/var/www/html/)
-- ❌ Database accessible at /database/test.db
+- ❌ Database accessible at /storage/test.db
 - ❌ Config files accessible
 - ❌ Dev server exposed everything
 - ❌ Relied on nginx deny rules
@@ -88,18 +88,18 @@ just serve
 # Test in browser:
 # - http://localhost:8000/ → Should work
 # - http://localhost:8000/admin/ → Should work
-# - http://localhost:8000/database/test.db → Should 404 ✅
+# - http://localhost:8000/storage/test.db → Should 404 ✅
 # - http://localhost:8000/config/ → Should 404 ✅
-# - http://localhost:8000/../database/test.db → Should 404 ✅
+# - http://localhost:8000/../storage/test.db → Should 404 ✅
 ```
 
 ### Security Verification
 ```bash
 # These should all return 404:
-curl http://localhost:8000/database/test.db
+curl http://localhost:8000/storage/test.db
 curl http://localhost:8000/config/bootstrap.php
 curl http://localhost:8000/vendor/autoload.php
-curl http://localhost:8000/../database/test.db
+curl http://localhost:8000/../storage/test.db
 curl http://localhost:8000/lib/Database.php
 ```
 
@@ -138,7 +138,7 @@ curl http://localhost:8000/lib/Database.php
    just server-status
    curl -I https://posterg.erg.be/
    curl -I https://posterg.erg.be/admin/
-   curl -I https://posterg.erg.be/database/test.db  # Must 404!
+   curl -I https://posterg.erg.be/storage/test.db  # Must 404!
    ```
 
 ## 📝 Path Reference
@@ -164,7 +164,7 @@ require_once LIB_ROOT . '/Database.php';               // Library
 - `PUBLIC_ROOT` - /path/to/posterg-website/public
 - `CONFIG_ROOT` - /path/to/posterg-website/config
 - `DATABASE_ROOT` - /path/to/posterg-website/database
-- `DATABASE_PATH` - /path/to/posterg-website/database/test.db
+- `DATABASE_PATH` - /path/to/posterg-website/storage/test.db
 - `RESOURCES_ROOT` - /path/to/posterg-website/resources
 - `LIB_ROOT` - /path/to/posterg-website/lib
 - `VAR_ROOT` - /path/to/posterg-website/var