agent: Improve the UX around interacting with MCP servers (#32622)

Still a work in progress! Todos before merging:

- [x] Allow to delete (not just turn off) an MCP server from the panel's
settings view
- [x] Also uninstall the extension upon deleting the server (check if
the extension just provides MCPs)
- [x] Resolve repository URL again
- [x] Add a button to open the configuration modal from the panel's
settings view
- [x] Improve modal UX to install and configure a non-extension MCP

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

crates/agent/Cargo.toml

@@ -36,6 +36,7 @@ convert_case.workspace = true
 db.workspace = true
 editor.workspace = true
 extension.workspace = true
+extension_host.workspace = true
 feature_flags.workspace = true
 file_icons.workspace = true
 fs.workspace = true
@@ -90,7 +91,6 @@ thiserror.workspace = true
 time.workspace = true
 time_format.workspace = true
 ui.workspace = true
-ui_input.workspace = true
 urlencoding.workspace = true
 util.workspace = true
 uuid.workspace = true