fix(windows): quote diff-pane argv so git receives the delta pager intact

[mathix420]

Why diffs still failed on Windows

#43's follow-up (f4ac7a4, shipped in v0.2.9) replaced the sh -c '… | delta' pipe with git -c "core.pager=delta --paging=always" diff …, which is correct — but on Windows alacritty_terminal flattens PTY argv into a single CreateProcess command line and only quotes arguments when Options::escape_args is set. We left it at the default false, so the command line came out as:

git -c core.pager=delta --paging=always diff -- <file>

The pager spec split on its internal space, git rejected --paging=always as an unknown global option and exited instantly, and reap_exited_sessions closed the pane the same frame — the diff panel "opened" and auto-closed without rendering anything. Any file path containing a space would have split identically.

Fix

Set escape_args: true for diff-pane sessions, whose argv is constructed in code and therefore carries logical arguments that must survive intact. Config-shell args from alacritty.toml stay raw (false), matching how upstream alacritty treats user-authored shell arguments on Windows.

No behavior change on unix: the field is #[cfg(windows)]-gated and unix PTYs exec a real argv.

Testing

• cargo check -p alacritree and cargo fmt clean on Linux; the Windows-gated field matches alacritty_terminal::tty::Options exactly (same pattern as its own test_cmdline, which asserts escape_args: true produces echo "hello world").
• Needs a Windows smoke test after merge: click staged/unstaged/untracked files and the branch diff row in the right sidebar; each should open delta in the pane instead of flashing closed.

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