Tauri CLI 2.0 DX Improvements

Issues related to https://github.com/tauri-apps/tauri-docs/pull/1365

Could we adjust a few things in the Tauri CLI to improve the DX:

• Add this (or similar) to help for dev:

This command will open the WebView in development mode. It makes use of the build.devPath property from your tauri.conf.json file.
If you have entered a command to the build.beforeDevCommand property, this one will be executed before the dev command.

• Add this (or similar) to help for info:

tauri info shows a concise list of information about the environment, Rust, Node.js and their versions as well as a few relevant project configurations.

• Add better copy for completions command:

The Tauri CLI can generate shell completions for Bash, Zsh, PowerShell and Fish.

Are there any instructions after running this command on how to actually make it kick into place? If so could we include those in either the help comments or log them out so the user isn't confused on why things aren't working? @FabianLars wrote some amazing things here that I think belongs in the CLI instead.

• Switch tauri plugin add to tauri add

We've talked about this on a few places and I've not heard anything against this, but open to discussion if needed. Basically let's simplify this stuff as much as possible. End users don't care so much about if it's a plugin, they care about the functionality.

Read the referenced tauri-docs pull request 1365 and the CLI documentation in src/content/docs/2/reference/cli.mdx, especially lines 292-424. Compare that guidance with the requested dev, info, completions, and add command changes, then verify that the help text and completion setup instructions cover the listed user questions and all checklist items are addressed.