fix: allow "/" as folder path for project root in write_note

Users reported that folder="/" doesn't work for writing to project root.
The validate_project_path() function was blocking "/" before sanitization.

Changes:
- Normalize "/" to "" before path validation in write_note tool
- Update documentation to show both "/" and "" work for root
- Add test case verifying "/" works as root folder path

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

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

Author: phernandez

src/basic_memory/mcp/tools/write_note.py

@@ -63,8 +63,8 @@ async def write_note(
         title: The title of the note
         content: Markdown content for the note, can include observations and relations
         folder: Folder path relative to project root where the file should be saved.
-                Use forward slashes (/) as separators. Use empty string ("") to write to project root.
-                Examples: "notes", "projects/2025", "research/ml", "" (root)
+                Use forward slashes (/) as separators. Use "/" or "" to write to project root.
+                Examples: "notes", "projects/2025", "research/ml", "/" (root)
         project: Project name to write to. Optional - server will resolve using the
                 hierarchy above. If unknown, use list_memory_projects() to discover
                 available projects.
@@ -125,6 +125,10 @@ async def write_note(
     # Get and validate the project (supports optional project parameter)
     active_project = await get_active_project(client, project, context)
 
+    # Normalize "/" to empty string for root folder (must happen before validation)
+    if folder == "/":
+        folder = ""
+
     # Validate folder path to prevent path traversal attacks
     project_path = active_project.home
     if folder and not validate_project_path(folder, project_path):

test-int/mcp/test_write_note_integration.py

@@ -397,6 +397,7 @@ async def test_write_note_file_path_os_path_join(mcp_server, test_project):
             "nested/folder/another-note",
         ),
         ("", "Root Note", "root-note.md", "root-note"),
+        ("/", "Root Slash Note", "root-slash-note.md", "root-slash-note"),
         (
             "folder with spaces",
             "Note Title",