fix: shell injection in hooks, Claude Code mining, chromadb pin

- hooks/mempal_save_hook.sh: pass $TRANSCRIPT_PATH as sys.argv
  instead of interpolating into python -c string (fixes #110)
- normalize.py: accept type "user" in addition to "human" for
  Claude Code JSONL sessions (fixes #111)
- convo_miner.py: skip tool-results/, memory/ dirs and .meta.json
  files when scanning for conversations (fixes #111)
- pyproject.toml: pin chromadb>=0.4.0,<1 to avoid crashing 1.x
  builds on macOS ARM64 (fixes #100)

hooks/mempal_save_hook.sh

@@ -81,10 +81,10 @@ fi
 
 # Count human messages in the JSONL transcript
 if [ -f "$TRANSCRIPT_PATH" ]; then
-    EXCHANGE_COUNT=$(python3 -c "
+    EXCHANGE_COUNT=$(python3 - "$TRANSCRIPT_PATH" <<'PYEOF'
 import json, sys
 count = 0
-with open('$TRANSCRIPT_PATH') as f:
+with open(sys.argv[1]) as f:
     for line in f:
         try:
             entry = json.loads(line)
@@ -98,7 +98,8 @@ with open('$TRANSCRIPT_PATH') as f:
         except:
             pass
 print(count)
-" 2>/dev/null)
+PYEOF
+2>/dev/null)
 else
     EXCHANGE_COUNT=0
 fi