Guard Pillow-dependent features

[PedroBMR]

Summary

• guard Pillow imports across compilation, imaging, rendering, and UI modules and raise clear runtime errors when Pillow is unavailable
• disable preview widgets and quick print previews when Pillow cannot be imported while keeping the application responsive
• ensure Pillow-requiring tests skip gracefully when the library is missing and document the runtime limitation in the README

Testing

• pytest -q

---

https://chatgpt.com/codex/tasks/task_e_68dbe9cc3a30832c954f15d561ceee71

[chatgpt-codex-connector]

💡 Codex Review

Labels-App/editor/widget.py

Lines 578 to 582 in c3c686a

	image = render_template(
	backend_dict,
	context,
	calibration=self.scene.calibration,
	)

[P1] Skip preview update when Pillow is unavailable

LabelEditorWidget._perform_preview_update calls render_template(...) unconditionally. When Pillow is not installed, the new guards in render.preview raise RuntimeError, so the editor still crashes during initialisation even though the UI disables preview controls when ImageQt is missing. Short-circuit this method or catch the exception when Pillow cannot be imported so the application can keep running without preview support.

---

Labels-App/editor/items/base.py

Lines 114 to 118 in c3c686a

	result = render_element_image(
	self._element,
	context,
	page,
	calibration=calibration,

[P1] Guard element pixmap updates when Pillow is missing

GraphicsElementItem._update_pixmap calls render_element_image(...) before checking whether Pillow is available. Because the renderer now raises a RuntimeError when Pillow is absent, loading any document still blows up instead of falling back to the placeholder UI. The method should skip or handle pixmap generation when ImageQt (and therefore Pillow) is unavailable.

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