Re-run pager-rendered diff output after resize

[SergioChan]

PR Description

Fixes #4415.

When a terminal resize happens while a diff is rendered through a PTY-backed pager (for example delta), lazygit previously only resized the PTY and kept the already-rendered pager output.

This change re-runs HandleRenderToMain() after resize whenever there are active PTY-backed views, so the current diff is regenerated using the new width.

Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc

Validation

• go test ./pkg/gui ./pkg/gui/controllers -run "TestScreenModeActions" -count=1
• go test ./pkg/gui/... (partially ran; unrelated pre-existing failures in pkg/gui/presentation and pkg/gui/style on this environment)