Harden maintainer-preview harness and review fixes

Unify conversational domain routing, preserve artifact completion evidence, replace provisional tool-round prose with terminal synthesis, and resolve verified maintainer review findings across search, frontend module identity, path policy, configuration, and built-in skill startup.

tests/test_yoyo_builtin_theme.py

@@ -0,0 +1,21 @@
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def test_yoyo_is_a_builtin_theme_with_its_saved_effect_defaults():
+    source = (ROOT / "static/js/theme.js").read_text(encoding="utf-8")
+
+    assert "yoyo:       { bg:'#211f23', fg:'#dfdbd7'" in source
+    assert "yoyo:       'ascii-fireflies'" in source
+    assert "yoyo:       '#b8e6c1'" in source
+    assert ".filter(([name]) => !THEMES[name])" in source
+
+
+def test_agent_theme_inventory_includes_yoyo():
+    interaction = (ROOT / "src/ai_interaction.py").read_text(encoding="utf-8")
+    schemas = (ROOT / "src/tool_schemas.py").read_text(encoding="utf-8")
+
+    assert '"monolith", "yoyo"' in interaction
+    assert "blueprint, monolith, yoyo" in schemas