Fix GNOME 50 shell crash when closing SearchLight on outside click

[BtraRahul]

Summary

• Fixes a GNOME Shell crash (SIGABRT) that occurred when opening SearchLight and clicking outside the empty search overlay on the homescreen, which dropped the session back to the GDM login screen.
• Defers show()/hide() actor-tree work out of input and focus handlers so Clutter 18 on GNOME 50 no longer aborts during _release_ui() teardown.
• Hides the overview search entry before detaching it and adds a re-entrancy guard on hide() to prevent nested teardown during focus changes.
• Scopes _remove_events() to show-session listeners only, so permanent enable() listeners (overview, app-state, window-created) survive after close.
• Adds a full-monitor click catcher so outside clicks close the overlay safely instead of passing through to the desktop.
• Updates overview signal wiring from deprecated overview-showing/overview-hidden to showing/hidden, improving GNOME 50 compatibility for overview tracking.

This addresses the same root cause discussed in #82, #133, and #166, and complements open PR #164.

Test environment

• OS: Ubuntu 26.04 LTS
• GNOME Shell: 50.1 (Wayland)
• Extension version tested: 102

Test plan

• Open SearchLight on empty homescreen and click outside — closes cleanly, no login screen
• Close via Escape key
• Toggle open/close via keyboard shortcut
• Toggle via panel icon
• Open/close repeatedly — overview tracking still works after first close
• Extension reloads without JS errors (gnome-extensions disable/enable search-light@icedman.github.com)
• Launch a search result from the overlay
• Verify on additional GNOME 50 setups if available

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