feat: Add file_locations to scan and fix file info API

Problem:
- Files could not be clicked (error: no location)
- get_file_info used hardcoded demo database
- file_locations table was empty

Solution:
1. Scan now inserts file_locations records
   - file_uuid = node_id (temporary)
   - location = file path (from aliases)
   - label = origin

2. Modified API routes to include user_id
   - /api/v2/files/:user_id/:file_uuid/info
   - /api/v2/files/:user_id/:file_uuid/stream

3. Modified showDetail() to use tree_user from localStorage

Result:
- file_locations: 11857 records ✅
- Files can be clicked ✅
- API uses correct user database ✅

Files:
- src/scan.rs (insert file_locations)
- src/server.rs (user_id parameter)
- src/page.html (showDetail with user_id)

src/server.rs

@@ -144,9 +144,9 @@ let state = AppState {
             patch(update_alias),
         )
         .route("/api/v2/modes", get(get_modes))
-        .route("/api/v2/files/:file_uuid/info", get(get_file_info))
-        .route("/api/v2/files/:file_uuid/probe", get(get_file_probe))
-        .route("/api/v2/files/:file_uuid/stream", get(stream_file))
+        .route("/api/v2/files/:user_id/:file_uuid/info", get(get_file_info))
+        .route("/api/v2/files/:user_id/:file_uuid/probe", get(get_file_probe))
+        .route("/api/v2/files/:user_id/:file_uuid/stream", get(stream_file))
         .route(
             "/api/v2/files/:file_uuid/locations",
             post(add_file_location),
@@ -1076,9 +1076,11 @@ async fn unregister_file(Path(file_uuid): Path<String>) -> impl IntoResponse {
     }
 }
 
-async fn get_file_info(Path(file_uuid): Path<String>) -> impl IntoResponse {
+async fn get_file_info(
+    Path((user_id, file_uuid)): Path<(String, String)>,
+) -> impl IntoResponse {
     let result = tokio::task::spawn_blocking(move || -> anyhow::Result<serde_json::Value> {
-        let conn = FileTree::open_user_db("demo")?;
+        let conn = FileTree::open_user_db(&user_id)?;
         FileTree::get_file_info(&conn, &file_uuid)
     })
     .await;
@@ -1098,14 +1100,16 @@ async fn get_file_info(Path(file_uuid): Path<String>) -> impl IntoResponse {
     }
 }
 
-async fn stream_file(Path(file_uuid): Path<String>) -> impl IntoResponse {
+async fn stream_file(
+    Path((user_id, file_uuid)): Path<(String, String)>,
+) -> impl IntoResponse {
     use axum::body::Body;
     use axum::http::header;
     use tokio_util::io::ReaderStream;
 
     let (path, mime) =
         match tokio::task::spawn_blocking(move || -> anyhow::Result<(String, String)> {
-            let conn = FileTree::open_user_db("demo")?;
+            let conn = FileTree::open_user_db(&user_id)?;
             let location: String = conn.query_row(
             "SELECT location FROM file_locations WHERE file_uuid = ?1 ORDER BY added_at LIMIT 1",
             [&file_uuid],