feat: implement agent list from REST API and simplify agent selection #9

Job	Run time
typecheck	59s
test-js	2m 18s
lint	58s
Rust tests (Linux)	8m 27s
Rust tests (macOS)	3m 48s
Rust tests (Windows)	13m 3s
Tauri build (${{ matrix.platform.name }})	0s
	29m 33s

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