fix(library-desk): fix entity linking path cleaning and longest-first matching

Two critical bug fixes for entity linking:

1. **Path cleaning**: Replace hardcoded "users/jpmschweitzer/" with regex pattern
   to handle any user namespace. Now properly cleans paths for all users.

2. **Longest-first matching**: Move protected_ranges computation inside entity loop
   to recompute after each entity is processed. Prevents nested links like
   [[Machine](/machine) Learning](/ml) when processing multi-word entities.

These fixes ensure entity linking works correctly across all users and prevents
nested markdown links when entity names overlap.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/library-desk/src/routers/entity_linking.py

@@ -289,14 +289,6 @@ def add_entity_links_to_content(
     # e.g., "Machine Learning" before "Machine"
     linkable_entities.sort(key=lambda x: len(x["name"]), reverse=True)
 
-    # Find all existing markdown links to protect them
-    link_pattern = r'\[([^\]]+)\]\([^\)]+\)'
-    existing_links = list(re.finditer(link_pattern, content))
-
-    # Create a list of protected ranges (start, end) for ENTIRE links (text + URL)
-    # This prevents linking entity names inside existing link URLs
-    protected_ranges = [(m.start(), m.end()) for m in existing_links]
-
     updated_content = content
     links_added = 0
 
@@ -309,10 +301,18 @@ def add_entity_links_to_content(
             continue
 
         # Create markdown link
-        # We'll link to the relative path without the "users/jpmschweitzer/" prefix
-        clean_path = entity_path.replace("users/jpmschweitzer/", "")
+        # Remove any "users/{username}/" prefix to get clean relative path
+        clean_path = re.sub(r'^users/[^/]+/', '', entity_path)
         markdown_link = f"[{entity_name}](/{clean_path})"
 
+        # Find all existing markdown links to protect them (recompute each iteration)
+        link_pattern = r'\[([^\]]+)\]\([^\)]+\)'
+        existing_links = list(re.finditer(link_pattern, updated_content))
+
+        # Create a list of protected ranges (start, end) for ENTIRE links (text + URL)
+        # This prevents linking entity names inside existing link URLs
+        protected_ranges = [(m.start(), m.end()) for m in existing_links]
+
         # Find all potential matches
         pattern = r'\b(' + re.escape(entity_name) + r')\b'
         matches = list(re.finditer(pattern, updated_content, flags=re.IGNORECASE))