clear_pane uses stale libtmux workaround and underreports destructive behavior

[tony]

Problem

clear_pane still carries an old workaround for libtmux 0.56-era behavior: it manually runs send-keys -R and then clear-history.

The project now depends on libtmux 0.58, where Pane.reset() deliberately sends reset and clear-history to the target pane. The tool also advertises non-destructive mutating annotations even though it clears scrollback.

Upstream reference

• libtmux 0.58 Pane.reset() sends send-keys -R and clear-history: https://github.com/tmux-python/libtmux/blob/v0.58.0/src/libtmux/pane.py#L2201-L2220
• libtmux 0.58 clear_history(): https://github.com/tmux-python/libtmux/blob/v0.58.0/src/libtmux/pane.py#L2167-L2194

Minimal local recreation

$ uv run pytest tests/test_pane_tools.py::test_clear_pane -q

Then inspect the tool annotations through tools/list; clear_pane currently reports destructiveHint=false.

Minimal fix

• Replace the two-call implementation with pane.reset().
• Use an annotation preset that marks the operation as state-losing/destructive.
• Update docs that describe clear_pane as two separate tmux commands.

Acceptance criteria

• clear_pane still resets visible terminal state and clears scrollback.
• clear_pane uses pane.reset() with libtmux 0.58+.
• Tool annotations no longer imply the operation is non-destructive.
• Existing clear-pane tests pass.