feat: default incremental=True for index_folder and index_repo

Full re-index on every call is wasteful for active development.
Incremental mode uses SHA-256 content hashing and safely falls back
to a full index when no existing index is found. Closes #33.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jgravelle

src/jcodemunch_mcp/tools/index_folder.py

@@ -230,7 +230,7 @@ def index_folder(
     storage_path: Optional[str] = None,
     extra_ignore_patterns: Optional[list[str]] = None,
     follow_symlinks: bool = False,
-    incremental: bool = False,
+    incremental: bool = True,
 ) -> dict:
     """Index a local folder containing source code.
 

src/jcodemunch_mcp/tools/index_repo.py

@@ -211,7 +211,7 @@ async def index_repo(
     use_ai_summaries: bool = True,
     github_token: Optional[str] = None,
     storage_path: Optional[str] = None,
-    incremental: bool = False,
+    incremental: bool = True,
 ) -> dict:
     """Index a GitHub repository.