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/page.html

@@ -717,11 +717,12 @@ function renderGrid(d,mode){
 // DETAIL PANEL
 function showDetail(fuuid){
     if(!fuuid)return;
+    var userId=localStorage.getItem("tree_user")||"demo";
     document.getElementById("mb-overlay").style.display="block";
     document.getElementById("mb-detail").style.display="block";
     var b=document.getElementById("mb-detail-body");
     b.innerHTML="<div style=text-align:center;padding:30px;color:#64748b>Loading...</div>";
-    fetch("/api/v2/files/"+fuuid+"/info").then(function(r){return r.json()}).then(function(d){
+    fetch("/api/v2/files/"+userId+"/"+fuuid+"/info").then(function(r){return r.json()}).then(function(d){
         var node=_td&&_td.nodes?_td.nodes.find(function(n){return n.file_uuid==fuuid}):null;
         var label=node?dname(node):fuuid;
         var sz=node?fsize(node.file_size):"-";