Stabilize core correctness and sync project plan state

src/atocore/ingestion/parser.py

@@ -17,10 +17,10 @@ class ParsedDocument:
     headings: list[tuple[int, str]] = field(default_factory=list)
 
 
-def parse_markdown(file_path: Path) -> ParsedDocument:
+def parse_markdown(file_path: Path, text: str | None = None) -> ParsedDocument:
     """Parse a markdown file, extracting frontmatter and structure."""
-    text = file_path.read_text(encoding="utf-8")
-    post = frontmatter.loads(text)
+    raw_text = text if text is not None else file_path.read_text(encoding="utf-8")
+    post = frontmatter.loads(raw_text)
 
     meta = dict(post.metadata) if post.metadata else {}
     body = post.content.strip()