Add coherent gobo presentation experiment (FogVolume / Vector Prism / Native Shadow) and fix projector + Visual Settings regressions

[PeramatoG]

Motivation

• Surface gobo projection was failing on Godot 4.7 because lights used for fixture beams were left with shadow_enabled = false, which produces black/stale light_projector output in this engine version.
• Visual Settings refresh could zero live beams by reconstructing scaled intensity from optional metadata (peraviz_beam_base_intensity) with a 0.0 default instead of falling back to held authoritative dimmer state.
• Provide an experiment to present gobo transmission coherently without creating per-gobo polygon explosion, while preserving the existing vector-prism fallback and a native-shadow workaround for fog shaping.

Description

• Ensure crisp surface projection by assigning the composed gobo texture to SpotLight3D.light_projector, enabling shadows only while a projector is active and restoring the previous shadow state on clear; add a reusable shadows-only aperture quad for the native-shadow experiment. (modified scripts/fixture_gobo_projector.gd)
• Add a Fog Volume presentation backend that places a per-emitter FogVolume cone, aligns it to Peraviz local -Z, projects the composed gobo texture through the volume, and uses an emission-based, zero-density presentation approximation to avoid cross-light fog coupling. (added/modified scripts/fog_volume_gobo_beam_controller.gd, scripts/shaders/fog_volume_gobo_beam.gdshader)
• Wire a selectable presentation mode into the volumetric renderer with three modes: Fog Volume Gobo (Experimental), Vector Gobo Prism (Reference), and Native Fog + Shadow Gobo (Experimental), and move deprecated/unused shader parameter writes out of the hot path. (modified scripts/beam_renderers/volumetric_beam_renderer.gd, scripts/beam_optics_controller.gd)
• Redesign Visual Settings UI to expose a single descriptive Beam presentation choice, rename Beam intensity to Beam / volume intensity, replace the old quick presets with experiment-oriented presets, and stop using the dead generic Beam quality control. (modified scripts/ui/visual/renderer_settings_panel.gd, scripts/visual_settings_window.gd)
• Fix Visual Settings refresh to use the last authoritative normalized_dimmer stored with the beam when recomputing scaled_intensity, and ensure presentation switches clean up previous backend resources (FogVolumes, mask quads) without leaking. (modified scripts/load_scene.gd)
• Add a headless GDScript test exercising projector lifecycle, open-slot clearing, shadows-only mask creation, and repeated A→B→C→A mode switching, plus documentation and release-note updates describing the experiment and Godot 4.7 limitations. (added tests/gdscript/test_gobo_presentation_modes.gd, updated docs/BEAM_RENDERING_MODES.md and docs/release-notes-draft.md)
• Small lifecycle/cleanup fixes: ensure FogVolume removal uses remove_child() before queue_free(), guard native-shadow preference per-presentation-mode, and avoid unnecessary vector fallback when no runtime gobo is present. (multiple script changes)

Files touched (high level): scripts/fixture_gobo_projector.gd, scripts/fog_volume_gobo_beam_controller.gd, scripts/beam_renderers/volumetric_beam_renderer.gd, scripts/beam_optics_controller.gd, scripts/load_scene.gd, scripts/ui/visual/renderer_settings_panel.gd, scripts/visual_settings_window.gd, scripts/shaders/fog_volume_gobo_beam.gdshader, tests/gdscript/test_gobo_presentation_modes.gd, docs/BEAM_RENDERING_MODES.md, docs/release-notes-draft.md (commit f2bb610).

Testing

• Ran repository checks tests/check_no_large_files.sh (passed with existing advisory warnings) and tests/check_runtime_architecture.sh (passed).
• Ran git diff --check (passed) and local static/grep validations to confirm removed dead UI/shader parameters; results OK.
• Added tests/gdscript/test_gobo_presentation_modes.gd covering projector shadow lifecycle, open-slot clearing, native-shadow mask creation, FogVolume ownership, and repeated-mode switching, but headless Godot execution in this environment failed because neither godot nor godot4 is installed (so the new GDScript test could not be executed here).
• Notes on environment test limitations: attempted headless execution with godot --headless --path . --script tests/gdscript/test_gobo_presentation_modes.gd and godot4 --headless --path . --script tests/gdscript/test_gobo_presentation_modes.gd, both returned not-found in CI environment.

If you want, I can: run the new headless test locally where Godot 4.7 is available, expand the tests to assert additional mode-specific visual/shader parameters, or trim/rename any UI labels before merging.

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Codex Task