[Feature] Review changes to a note since a checkpoint, with each change labeled by its source #919

Problem

ZenNotes has no way to review what changed in a note since a given point, or where each change came from.

This matters most when AI agents edit a vault through the MCP server. After an agent edits a note, there is no way to see the changes inside ZenNotes, so they either go unreviewed or get checked in another tool. I've been using Git with my vault to solve this, the same way developers review the code that coding agents write. It works, but every review means leaving ZenNotes for a diff viewer.

The same need applies to edits that don't come from agents. A note can also change from the desktop or web app, the mobile apps, the TUI, or an external editor such as Neovim or VS Code. If only MCP edits were recorded, a manual edit made between two agent edits would either be missing from the review or show up as part of the agent's change, and the user couldn't tell who changed what. Recording every edit, whatever its source, keeps the review accurate. It also makes the feature useful on its own for manual edits, such as reviewing a long rewrite or tracking down an unexpected change.

Proposed solution

A way to review the changes to a note since a checkpoint:

• Marking a note as reviewed sets a checkpoint. Only that explicit action moves it; opening or viewing a note does not.
• A diff shows every change made since the checkpoint, across sessions and days.
• Each change shows when it was made and where it came from: the app (desktop, web, or mobile), the TUI, an MCP client by name (for example, Claude Code), or an external editor such as Neovim or VS Code.
• Each change can be kept or reverted on its own.
• A comment can be attached to a specific change. Agents can already read comments through MCP, so this would let users give an agent feedback on its edit without leaving ZenNotes.
• It works with local vaults, ZenNotes Cloud vaults, and self-hosted server vaults.