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/scan.rs

@@ -224,6 +224,18 @@ pub fn scan_directory(user_id: &str, dir: &str, batch_size: usize, options: Scan
     
     for node in file_nodes {
         insert_node(&conn, &node)?;
+        
+        if let Some(ref file_uuid) = node.file_uuid {
+            let path = node.aliases.get("path").cloned().unwrap_or_default();
+            if !path.is_empty() {
+                conn.execute(
+                    "INSERT OR IGNORE INTO file_locations (file_uuid, location, label, added_at)
+                     VALUES (?1, ?2, 'origin', ?3)",
+                    rusqlite::params![file_uuid, path, chrono::Utc::now().timestamp().to_string()],
+                )?;
+            }
+        }
+        
         inserted += 1;
         
         if inserted % batch_size == 0 {