feat: per-theme Jinja env enables theme-level macro override

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

tests/test_theme_registry.py

@@ -37,3 +37,20 @@ def test_discover_fails_fast_when_themes_dir_missing(tmp_path, monkeypatch):
     import pytest
     with pytest.raises(RuntimeError, match='themes directory missing'):
         core.discover_themes()
+
+def test_env_for_theme_prefers_theme_dir_then_shared_root():
+    from app import theme_pro
+    env = theme_pro.env_for('industrial')
+    paths = [str(p).replace('\\', '/') for p in env.loader.searchpath]
+    assert paths[0].endswith('themes/industrial')
+    assert paths[1].endswith('themes')
+    # 共享宏库必须仍可解析（回落路径）
+    assert env.get_template('_professional_components.html') is not None
+
+def test_env_for_is_cached_per_theme():
+    from app import theme_pro
+    assert theme_pro.env_for('industrial') is theme_pro.env_for('industrial')
+
+def test_env_for_pro_template_loads_unprefixed():
+    from app import theme_pro
+    assert theme_pro.env_for('industrial').get_template('pro.html') is not None