v0.5.2

Three changes since v0.5.1.

• A streaming thought holds its height. The two rows under ✻ Thinking… were the last two lines of the thought, wrapped afterwards — a paragraph is one line, so the block was any number of rows and changed on every delta, and the whole transcript above it moved with it (reported on Windows, where a narrower console made it worse; the same everywhere). The tail is now measured in rows as drawn: exactly two while a thought streams, three under a running tool, whatever the width. Plan M77.
• A spawn names the level it thinks at. SpawnAgent takes thinking beside model and provider, a child inherits the parent's level unless told otherwise, off is a level, and a SetThinking tool lets an agent move its own or a child's mid-run. The level rides the session spec, so session/open on the wire and the next turn agree. ADR-0047, plan M76.
• An attached client may open the browser itself. BINGO_BROWSER_MODE=client tells ShowPage and login to hand the URL to the client instead of spawning the platform opener; BINGO_NO_BROWSER still wins. ADR-0046.