Add visual whitespace indicators to diff and staging views

[themactep]

Toggle with <c-v> to render spaces as middle dots (·) and tabs as right arrows (→ followed by dashes to fill the tab stop) in diffs, staging, patch building, and merge conflict views.

Config

• gui.showWhitespace (default false) — enable permanently
• keybinding.universal.toggleShowWhitespace (default <c-v>)

Implementation

• pkg/utils/show_whitespace.go — ANSI-aware whitespace character replacement
• pkg/gui/view_helpers.go — string-based view filtering
• pkg/gui/tasks_adapter.go — PTY/streaming writer filter
• pkg/gui/controllers/toggle_show_whitespace_action.go — toggle action
• pkg/gui/context/patch_explorer_context.go — patch explorer
• pkg/gui/context/merge_conflicts_context.go — merge conflicts
• pkg/gui/controllers/helpers/staging_helper.go — staging views
• pkg/gui/controllers/helpers/patch_building_helper.go — patch building
• pkg/gui/controllers/local_commits_controller.go — custom patch panel
• vendor/github.com/jesseduffield/gocui/view.go — lineWrap recognizes · as break point
• pkg/utils/lines.go — WrapViewLinesToWidth recognizes · as break point

Markers render with ANSI faint (\x1b[2m) for subtle appearance.

[themactep]

and here's how it works
https://github.com/user-attachments/assets/ae533340-e2de-43ef-9bb7-bbee7986d240