fix(guide): keep the guide line from collapsing the layout

[laurigates]

Problem

The TUI stacks four panes vertically: query editor, guide, completion, and JSON viewer. The guide line shows transient status messages (result: …, jq failed: …, copy notifications, etc.).

When there was no message to show, the guide was rendered from an empty status::State, which produces zero rows. The renderer drops zero-row panes entirely (Terminal::draw filters out panes whose wrapped_lines is empty), so the guide line disappeared and the JSON viewer slid up by one row. As soon as a status message appeared, the pane reclaimed its row and pushed everything back down.

The result: on every keystroke that toggled a status message on or off, the entire JSON view jumped up and down — distracting during normal editing.

Fix

Reserve the guide line as a single blank row whenever there is no message, so the pane never collapses to zero rows and the panes below it stay put:

• GuideAction::Clear now renders one blank line instead of an empty state.
• The initial render reserves the same blank row, so the layout is stable from the first frame (previously the first status message would shift everything down).

--no-hint is unchanged: the guide stays permanently empty (consistently zero rows), so there is no jump in that mode either.

Testing

• cargo fmt --all -- --check
• cargo clippy
• cargo test
• cargo build --bins

All pass. The behavior is a TUI layout change best confirmed interactively: type a filter that toggles between valid and invalid (e.g. . → .foo → . ) and observe the JSON view no longer jumps as the status line appears/disappears.