feat(client): add visual test harness with golden regression

Gives Claude eyes: `make screenshot` captures a rendered frame,
`make test-visual` compares against golden PNGs, `make visual-update`
regenerates goldens. Built to debug the Sprint 22 fog regression and
prevent future visual regressions across fog, HUD, dialogue, and UI.

Config-driven via tests/visual.json (11 scenarios, 2 flows).
Capture engine boots main.tscn with real GPU rendering (not --headless),
waits for NoiseTexture2D async gen, uses deterministic shader time.

Components:
- visual_capture.gd: SceneTree capture engine (scenario + movie modes)
- visual_scenarios.gd: per-scenario setup hooks
- tooling/visual-diff: pixel comparator (PIL primary, struct fallback)
- tooling/visual-thumbnail: contact sheet + crop tool
- tests/run-visual: suite script (xvfb wrapping, golden workflow)
- fog_state.gd: override_time for deterministic captures
- fog_shader.gd: fog_noise_ready signal for settle sequencing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Makefile

@@ -8,7 +8,8 @@ GODOT := $(shell command -v godot4 2>/dev/null || command -v godot 2>/dev/null)
        fixtures-client golden-diff golden-update \
        checklist-validate checklist-generate \
        perf-baseline debug-schedule \
-       test-ipc-fixtures test-ipc-protocol test-ipc-integration test-ipc-benchmark
+       test-ipc-fixtures test-ipc-protocol test-ipc-integration test-ipc-benchmark \
+       screenshot visual-movie test-visual visual-update
 
 # --- Configuration ---
 
@@ -53,6 +54,11 @@ help:
 	@echo "  make checklist-generate Validate checklists + print condition summary"
 	@echo "  make perf-baseline      Run performance benchmarks and save baseline"
 	@echo ""
+	@echo "  make screenshot          Ad-hoc visual capture (SCENARIO=name, default: fog_3state)"
+	@echo "  make visual-movie       Flow capture with contact sheet (FLOW=name)"
+	@echo "  make test-visual        Run visual golden regression tests"
+	@echo "  make visual-update      Regenerate visual goldens and stage for commit"
+	@echo ""
 	@echo "  make pre-pr             Run all pre-PR checks (lint, build, test, validate, fixtures)"
 	@echo "  make pre-pr-server      Server-scoped pre-PR (lint, build, test, fixtures)"
 	@echo "  make pre-pr-client      Client-scoped pre-PR (lint, build, test)"
@@ -318,6 +324,20 @@ debug-schedule:
 	@echo "Dumping bevy_ecs schedule graph..."
 	@cd server && cargo run --bin settled-reach-server -- --dump-schedule
 
+# --- Visual test harness ---
+
+screenshot:
+	@tests/run-visual --screenshot $(SCENARIO)
+
+visual-movie:
+	@tests/run-visual --movie $(FLOW)
+
+test-visual:
+	@tests/run-visual
+
+visual-update:
+	@tests/run-visual --update
+
 content-ron:
 	cd tooling/content-converter && cargo build --release
 	tooling/content-converter/target/release/content-converter --input content --output content-ron --verbose