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-hunk-tracker/src/actor/file_utils.rs

@@ -318,6 +318,7 @@ mod tests {
         assert!(matches!(state, FileContentState::TooLarge { .. }));
     }
 
+    #[cfg(unix)]
     #[tokio::test]
     async fn test_read_file_bounded_symlink() {
         let dir = tempfile::tempdir().unwrap();