fix: focus pane on left-click even when mouse reporting is active

The Down(Left) handler called forward_pane_mouse_button before focus_pane
and early-returned when the forward succeeded, which happens for any pane
running a TUI that has enabled mouse reporting (e.g. Claude Code). As a
result, clicking such a pane forwarded the click to the inner TUI but
never updated herdr's focus state, leaving the previous pane highlighted.

Reorder the handler to focus first and forward after, matching the
pattern already used by handle_terminal_wheel. Shells and TUIs without
mouse reporting (e.g. Codex) were unaffected because their forward
returned false and the focus update happened in the fallthrough branch.

Add a regression test that installs a pane runtime with mouse reporting
enabled via the '\x1b[?1002h' DECSET sequence and asserts that a
Down(Left) event retargets focus.

0 files changed, 0 insertions, 0 deletions