v0.6.0

Added

• README screenshots (dark and light), rendered deterministically from the
  headless TUI via the ignored dump_screenshot test (cargo test dump_screenshot -- --ignored).
• Compose an annotation in $EDITOR: Ctrl-e in the annotation editor suspends
  the TUI and opens the body in $VISUAL/$EDITOR (falling back to vi), seeded
  below a marker line; saving feeds the text back. The ignored block above the
  marker quotes the annotated source lines for reference. Everything above the
  marker is ignored.
• Trigger a headless coding agent from the TUI: c hands the focused annotation
  to a claude session, C hands it every open annotation, and L toggles a
  log panel below the diff that streams the session's assistant messages and tool calls. The
  status line tracks progress and markers flip live as the agent records
  outcomes; the session is non-blocking. The agent inherits the environment (so
  CLAUDE_CONFIG_DIR/PATH reach it), and MARGIN_AGENT_CMD overrides the
  command.

Changed

• The annotation editor now supports in-buffer cursor movement and editing:
  character/line motion (arrows), word motion (Ctrl-←/Ctrl-→), line ends
  (Home/End), and Del / Ctrl-w deletion. Typing and Backspace act at the
  cursor instead of only at the end.

Fixed

• The commit list/message divider in the top band now lines up with the
  split-diff divider below it. The two were off by one column.