Add :vault_prepend MCP tool

[hakeem0114]

Summary

Add a vault_prepend MCP tool that prepends content to the beginning of a vault file. This would complement the existing vault_append MCP tool.

Motivation

Some Obsidian workflows organize notes with the newest entries first, such as inboxes, journals, and activity logs.

While vault_patch is useful for targeted Markdown modifications, there is currently no simple raw file operation equivalent to vault_append for inserting content at the beginning of a file.

Implementation

Before:

- [ ] Existing task 1
- [ ] Existing task 2

Calling:

{
  "filepath": "Tasks.md",
  "content": "- [ ] New task\n"
}

Would result in:

- [ ] New task
- [ ] Existing task 1
- [ ] Existing task 2