feat: fix mods tab, add client/server split, and scaffold server dirs

Mods tab bug fixes:
- mod_manager: fix wrong kwargs in set_enabled_mods, fix scan dir to use
  mods/ subdir instead of server root, migrate old string-list format to
  dict format on read
- service: replace dead server_mods SQL JOIN with get_enabled_mods()
  call through the mod_manager capability; pass is_server_mod to
  build_mod_args
- mods_router: accept list[EnabledModEntry] objects (name + is_server_mod)
  instead of bare strings

Client/server mod split:
- Mods now stored as list[{"name": str, "is_server_mod": bool}]; old
  string-list format auto-migrated on read
- is_server_mod=true routes to -serverMod= arg; false to -mod= arg
- ModList UI: amber Client/Server badge in selected pane; toggle button
  in split-pane selector

Directory scaffold:
- process_config: adds "mods" to dir layout; provides get_dir_readme()
  with per-directory README.txt content
- file_utils: ensure_server_dirs() gains readme_provider kwarg; writes
  README.txt idempotently if absent
- service.create_server: passes readme_provider via hasattr probe
- main.py startup: backfills all existing servers with correct subdirs
  and README files (idempotent)

Docs: API.md and FRONTEND.md updated for new mod schema and types
Test __init__.py files added for pytest discovery

API.md

@@ -1374,18 +1374,30 @@ List all available mods and which are currently enabled for this server.
     "mods": [
       {
         "name": "@CBA_A3",
-        "folder_path": "C:/Arma3Server/@CBA_A3",
-        "enabled": true
+        "path": "D:/Arma3Server/1/mods/@CBA_A3",
+        "size_bytes": 12345678,
+        "enabled": true,
+        "is_server_mod": false,
+        "display_name": "Community Base Addons A3",
+        "workshop_id": "450814997"
       },
       {
         "name": "@ACRE2",
-        "folder_path": "C:/Arma3Server/@ACRE2",
-        "enabled": true
+        "path": "D:/Arma3Server/1/mods/@ACRE2",
+        "size_bytes": 9876543,
+        "enabled": true,
+        "is_server_mod": true,
+        "display_name": "ACRE2",
+        "workshop_id": "751965892"
       },
       {
         "name": "@USAF",
-        "folder_path": "C:/Arma3Server/@USAF",
-        "enabled": false
+        "path": "D:/Arma3Server/1/mods/@USAF",
+        "size_bytes": 55000000,
+        "enabled": false,
+        "is_server_mod": false,
+        "display_name": null,
+        "workshop_id": null
       }
     ]
   },
@@ -1393,6 +1405,8 @@ List all available mods and which are currently enabled for this server.
 }
 ```
 
+Mod folders are scanned from `{server_data_dir}/{server_id}/mods/@*`. `display_name` is parsed from `mod.cpp`; `workshop_id` from `meta.cpp`. `is_server_mod: true` means the mod is passed via `-serverMod=` instead of `-mod=`.
+
 ---
 
 ### PUT /servers/{server_id}/mods/enabled
@@ -1405,13 +1419,18 @@ Set the list of enabled mods. This **replaces** the entire enabled list — send
 
 ```json
 {
-  "mods": ["@CBA_A3", "@ACRE2"]
+  "mods": [
+    { "name": "@CBA_A3", "is_server_mod": false },
+    { "name": "@ACRE2",  "is_server_mod": true  }
+  ]
 }
 ```
 
-| Field  | Type          | Required | Description                        |
-|--------|---------------|----------|------------------------------------|
-| `mods` | array[string] | Yes      | Complete list of mod names to enable |
+| Field               | Type    | Required | Description |
+|---------------------|---------|----------|-------------|
+| `mods`              | array   | Yes      | Complete list of mod entries to enable |
+| `mods[].name`       | string  | Yes      | Mod folder name (must start with `@`) |
+| `mods[].is_server_mod` | bool | No       | `true` → `-serverMod=`, `false` (default) → `-mod=` |
 
 **Response 200:**
 
@@ -1420,7 +1439,10 @@ Set the list of enabled mods. This **replaces** the entire enabled list — send
   "success": true,
   "data": {
     "message": "Enabled mods updated. Restart the server for changes to take effect.",
-    "enabled_mods": ["@CBA_A3", "@ACRE2"]
+    "enabled_mods": [
+      { "name": "@CBA_A3", "is_server_mod": false },
+      { "name": "@ACRE2",  "is_server_mod": true  }
+    ]
   },
   "error": null
 }