Add image/attachment support in preview mode

- Fetch attachments via WebDAV using Tauri HTTP plugin (bypasses CORS)
- Parse markdown for image references and convert to base64 data URLs
- In-memory cache to avoid re-fetching images
- Loading indicator while images load
- Register tauri-plugin-http in Rust builder
- Add HTTP permissions in capabilities

src-tauri/Cargo.toml

@@ -23,4 +23,5 @@ tauri-plugin-opener = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 tauri-plugin-dialog = "2.6.0"
+tauri-plugin-http = "2.5.7"
 

src-tauri/capabilities/default.json

@@ -5,6 +5,14 @@
   "windows": ["main"],
   "permissions": [
     "core:default",
-    "opener:default"
+    "opener:default",
+    "http:default",
+    {
+      "identifier": "http:default",
+      "allow": [
+        { "url": "https://*" },
+        { "url": "http://*" }
+      ]
+    }
   ]
 }

src-tauri/src/lib.rs

@@ -9,6 +9,7 @@ pub fn run() {
     tauri::Builder::default()
         .plugin(tauri_plugin_opener::init())
         .plugin(tauri_plugin_dialog::init())
+        .plugin(tauri_plugin_http::init())
         .invoke_handler(tauri::generate_handler![greet])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");