chore(gates): finish the Windows sweep — zero clippy findings workspace-wide

Second layer of platform gaps the mac/linux-only gate history left:
unix-only test imports/helpers now cfg-gated (mermaid, fast-worktree,
hunk-tracker, pager-render link test, three pty_e2e module decls),
clippy-suggested cleanups in Windows-cfg code (file-utils classifier,
tui console-mode restore, shared clipboard arboard-error flow, tools
terminal closure, workspace capability tail), and `cargo update` of h2
(RUSTSEC-2026-0258) and webbrowser (RUSTSEC-2026-0257) so `cargo deny
check advisories` passes again.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KSy9S31pZNWXtRZNVJ1sDf

crates/codegen/kigi-tui/tests/pty_e2e_scroll_selection.rs

@@ -66,5 +66,6 @@ mod wheel_flood_paints_no_ghost_frames;
 mod wheel_overscroll_at_bottom_reengages_follow_mid_stream;
 #[path = "pty_e2e/wheel_scrolls_viewport_during_streaming_turn.rs"]
 mod wheel_scrolls_viewport_during_streaming_turn;
+#[cfg(unix)]
 #[path = "pty_e2e/word_select_tip_on_double_click_pty.rs"]
 mod word_select_tip_on_double_click_pty;