Add --no-summaries flag for cost-free indexing

Allows indexing conversations without AI summary generation.
Still generates embeddings locally for semantic search.

Usage: index-conversations --cleanup --no-summaries

Changes:
- Added --no-summaries flag parsing in index-cli.ts
- Updated indexConversations, indexSession, indexUnprocessed to accept noSummaries param
- Changed indexUnprocessed to check database instead of summary file existence
- Updated help text with new flag and examples

This enables indexing large conversation archives without API costs.

skills/collaboration/remembering-conversations/tool/index-conversations

@@ -22,6 +22,7 @@ COMMANDS:
 OPTIONS:
   --concurrency N    Parallel summarization (1-16, default: 1)
   -c N               Short form of --concurrency
+  --no-summaries     Skip AI summary generation (free, but no summaries in results)
   --help, -h         Show this help
 
 EXAMPLES:
@@ -31,6 +32,9 @@ EXAMPLES:
   # Index with 8 parallel summarizations (8x faster)
   index-conversations --cleanup --concurrency 8
 
+  # Index without AI summaries (free, fast)
+  index-conversations --cleanup --no-summaries
+
   # Check index health
   index-conversations --verify