Backends for the Inspector and Reasoning panes beyond the generic CLI backend.

v0.13.0 - Agent Backends

Done	Area	Item
⬜	AGENT	Inspector / Reasoning follow-ups - host-tools bridge and OpenAI-compatible HTTP still planned. Provider-specific CLI adapters follow the v0.5.2 generic CliBackend lane: documented hooks/extensions only, never token reuse or TUI scraping.