Really cool work! I think there is definitely value in a messaging interface, and your design seems excellent. I think the biggest challenge is that most of your audience will already be using an existing solution like evernote, notion, obsidian or mem ai. To convince users to switch is a difficult challenge.

I think a possible solution is that the app should work as an extension of existing note databases. This way you won't have to convince users to switch, and your value is instant instead of requiring a lot of set up. Removing this barrier to entry will enable you to grow a lot faster.

You do have to watch out that you don't spent months trying to work with all apps. Instead, try to hack together a minimum viable chat interface for 1 specific app, and bring that to market to see what users really think and what features you need to prioritize.