feat: add file storage service with content-addressed blob store

Add FileStorageService for DXF/PDF storage using content hashing,
FileStorageOptions config, FilesController for uploads, and
FileBrowserController for browsing stored files.

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

FabWorks.Api/Properties/launchSettings.json

@@ -13,7 +13,7 @@
       "commandName": "Project",
       "dotnetRunMessages": true,
       "launchBrowser": true,
-      "launchUrl": "weatherforecast",
+      "launchUrl": "",
       "applicationUrl": "http://localhost:5206",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development"
@@ -23,7 +23,7 @@
       "commandName": "Project",
       "dotnetRunMessages": true,
       "launchBrowser": true,
-      "launchUrl": "weatherforecast",
+      "launchUrl": "",
       "applicationUrl": "https://localhost:7182;http://localhost:5206",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development"
@@ -32,7 +32,7 @@
     "IIS Express": {
       "commandName": "IISExpress",
       "launchBrowser": true,
-      "launchUrl": "weatherforecast",
+      "launchUrl": "",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development"
       }