Detailed graphics pass: authored textures, humanoid NPCs, HUD feedback, asset pipeline

- tools/generate_textures.py (deterministic PIL) produces all authored PNGs:
  brick facade, concrete, asphalt, awning, skyline, vignette, HUD icons,
  access-card art (all <=1024px, power-of-two)
- WorldBuilder: textured facade/glass door/sidewalk/asphalt, striped awning
  with 'STEP LINE', generated skyline backdrop planes
- GameManager: soft sun shadows (4-split parallel); guard in 'guard' group
- NPC avatars: humanoid rig (torso/head/limbs) with archetype props (camera,
  delivery box, performer hat, protest sign, tourist backpack), procedural
  walk bob, head-turns-toward-guard attention cue
- HUD: inspection artifact cards, mode icons (flashlight/door/wand),
  per-escalation vignette, body-camera overlay (corner brackets + REC + clock)
- assets/ import convention documented; test_asset_textures_present_and_pow2
  guards the pipeline (57 tests pass)
- README tech stack updated for Gitea Actions + asset pipeline; screenshot
  gallery regenerated (day + night)

src/test/tests/test_world.gd

@@ -45,6 +45,39 @@ func test_street_lamps_and_marquee_built() -> bool:
 	root.free()
 	return a and b and TestUtils.check(night_on, "lamps brighten at night") and TestUtils.check(day_off, "lamps dim in daylight")
 
+func test_asset_textures_present_and_pow2() -> bool:
+	var required := [
+		"res://assets/textures/brick_facade.png",
+		"res://assets/textures/concrete.png",
+		"res://assets/textures/asphalt.png",
+		"res://assets/textures/awning.png",
+		"res://assets/textures/skyline.png",
+		"res://assets/textures/vignette.png",
+		"res://assets/textures/icons/flashlight_on.png",
+		"res://assets/textures/icons/door_locked.png",
+		"res://assets/textures/icons/wand.png",
+		"res://assets/textures/icons/rec_dot.png",
+		"res://assets/textures/cards/id_card.png",
+		"res://assets/textures/cards/wristband.png",
+		"res://assets/textures/cards/ticket.png",
+		"res://assets/textures/cards/credential.png",
+		"res://assets/textures/cards/guest_list.png",
+	]
+	for path in required:
+		if not FileAccess.file_exists(path):
+			return TestUtils.fail("missing generated asset: %s — run tools/generate_textures.py" % path)
+	var img := Image.new()
+	for path in required:
+		if img.load(path) != OK:
+			return TestUtils.fail("cannot decode asset: %s" % path)
+		var w := img.get_width()
+		var h := img.get_height()
+		if w > 1024 or h > 1024:
+			return TestUtils.fail("asset too large: %s (%dx%d)" % [path, w, h])
+		if (w & (w - 1)) != 0 or (h & (h - 1)) != 0:
+			return TestUtils.fail("asset not power-of-two: %s (%dx%d)" % [path, w, h])
+	return true
+
 func test_door_indicator_built() -> bool:
 	var root := Node3D.new()
 	var builder := WorldBuilder.new(root)