Remove Operator widget count from title

[edwin-zvs]

Summary

• Remove the positional 1/3 prefix from Matrix-rain Operator widget viewport titles.
• Keep widget selection represented by the square title-bar indicators instead.
• Add a regression assertion that multi-widget rendering does not include the count prefix.

Tests

• cargo test -p agentd-cli operator_matrix_widgets_render_without_unbounded_padding
• cargo build
• git diff --check