feat: add content targets and loop expansion for target templates

Content targets write literal text to files via 'content:' field,
without requiring an AI provider or API keys. They are not archived
when overwritten.

Loop expansion allows defining 'loops:' at the top level with named
lists of values. Targets with [var] in their name are expanded via
cartesian product. Variables are substituted in all string fields.
Explicit targets override expanded ones. Escaping: \[var] -> [var].
Expansion happens at config load time so the rest of the system
(builder, graph, state) sees only expanded targets.

tests/test_config.py

@@ -84,6 +84,41 @@ class TestLoadConfig:
         with pytest.raises(Exception):
             _ = load_config(config_path)
 
+    def test_config_with_loops(self, project_dir: Path) -> None:
+        config_path = project_dir / "test.hokusai.yaml"
+        _ = config_path.write_text(
+            yaml.dump(
+                {
+                    "loops": {"a": [1, 2]},
+                    "targets": {"file-[a].txt": {"content": "Value [a]"}},
+                }
+            )
+        )
+        config = load_config(config_path)
+
+        assert "file-1.txt" in config.targets
+        assert "file-2.txt" in config.targets
+        assert "file-[a].txt" not in config.targets
+
+        t1 = config.targets["file-1.txt"]
+        assert isinstance(t1, ContentTargetConfig)
+        assert t1.content == "Value 1"
+
+    def test_config_loops_normalize_values_to_strings(self, project_dir: Path) -> None:
+        config_path = project_dir / "test.hokusai.yaml"
+        _ = config_path.write_text(
+            yaml.dump(
+                {
+                    "loops": {"x": [True, 3.14]},
+                    "targets": {"out-[x].txt": {"content": "[x]"}},
+                }
+            )
+        )
+        config = load_config(config_path)
+
+        assert "out-True.txt" in config.targets
+        assert "out-3.14.txt" in config.targets
+
     def test_content_target(self, project_dir: Path) -> None:
         config_path = project_dir / "test.hokusai.yaml"
         _ = config_path.write_text(