Bug: Mutable default arguments in function signatures

[gkorland]

Description

Several functions use mutable default arguments, a classic Python bug where mutations to the default value are shared across all calls:

1. api/project.py:96 — process_git_history:

   def process_git_history(self, ignore: Optional[List[str]] = []) -> GitGraph:

2. api/analyzers/source_analyzer.py:184 — analyze_local_folder:

   def analyze_local_folder(self, path: str, g: Graph, ignore: Optional[list[str]] = []) -> None:

3. api/graph.py:482 — connect_entities:

   def connect_entities(self, relation: str, src_id: int, dest_id: int, properties: dict = {}) -> None:

Impact

If any of these functions mutate their default argument (e.g., ignore.append(...) or properties['key'] = ...), the mutation persists across subsequent calls, causing hard-to-debug state leakage.

Suggested Fix

Use None as the default and create a new list/dict inside the function:

def process_git_history(self, ignore: Optional[List[str]] = None) -> GitGraph:
    if ignore is None:
        ignore = []

Note: analyze_sources in project.py already uses this pattern correctly.

Context

Found during code review of PR #522.