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-shared/src/clipboard.rs

@@ -1164,6 +1164,7 @@ mod platform {
 #[cfg(not(target_os = "macos"))]
 mod platform {
     use super::ImageData;
+    #[cfg(target_os = "linux")]
     use std::process::{Command, Stdio};
 
     /// No subprocess-free pasteboard probe exists off-macOS.
@@ -1926,19 +1927,18 @@ mod platform {
     // Public API
 
     pub fn get_text() -> anyhow::Result<Option<String>> {
-        let mut arboard_error = None;
-        match arboard_get_text() {
+        let arboard_error = match arboard_get_text() {
             Ok(Some(text)) => return Ok(Some(text)),
             // Wayland-only: arboard's empty answer is not authoritative,
             // fall through to wl-paste (see `wayland_tool_selected`).
             #[cfg(target_os = "linux")]
-            Ok(None) if wayland_tool_selected(linux_tool_spec()) => {}
+            Ok(None) if wayland_tool_selected(linux_tool_spec()) => None,
             Ok(None) => return Ok(None),
             Err(e) => {
                 tracing::debug!("arboard get_text failed: {e}");
-                arboard_error = Some(e);
+                Some(e)
             }
-        }
+        };
         #[cfg(target_os = "linux")]
         if let Some(spec) = linux_tool_spec() {
             let bytes = run_capture_out_checked(spec.read_text, CLI_READ_WAIT)?;
@@ -2039,19 +2039,18 @@ mod platform {
     }
 
     pub fn get_image() -> anyhow::Result<Option<ImageData>> {
-        let mut arboard_error = None;
-        match arboard_get_image() {
+        let arboard_error = match arboard_get_image() {
             Ok(Some(image)) => return Ok(Some(image)),
             // Wayland-only: arboard's empty answer is not authoritative,
             // fall through to wl-paste (see `wayland_tool_selected`).
             #[cfg(target_os = "linux")]
-            Ok(None) if wayland_tool_selected(linux_tool_spec()) => {}
+            Ok(None) if wayland_tool_selected(linux_tool_spec()) => None,
             Ok(None) => return Ok(None),
             Err(e) => {
                 tracing::debug!("arboard get_image failed: {e}");
-                arboard_error = Some(e);
+                Some(e)
             }
-        }
+        };
         #[cfg(target_os = "linux")]
         if let Some(spec) = linux_tool_spec()
             && let Some(argv) = spec.read_png