Add venv/.venv to ingestion's SKIP_DIRECTORIES

The previous fix (403b4e8) filtered doc-file selection through
should_skip_path(), assuming it matched tree_sitter_indexer.py's
exclusion behavior. It doesn't: ingestion.py's own SKIP_DIRECTORIES
never included 'venv'/'.venv' at all - only tree_sitter_indexer.py's
separate SKIP_DIRS did. Two inconsistent exclusion lists in the
codebase, and the previous fix happened to reuse the incomplete one.

Confirmed live: a selective-indexing run after the previous fix still
pulled in 61 .venv/lib/python3.11/site-packages/... files into
Ody-project_index.

app/core/ingestion.py

@@ -326,6 +326,8 @@ def ingest_documents(
 # Directories to always skip during ingestion
 SKIP_DIRECTORIES = {
     'node_modules',
+    'venv',
+    '.venv',
     '.git',
     '.svn',
     '.hg',