feat(query): add query classification handlers and metrics/entry points

[Nurysso]

Complete router handler implementations with structured query routing:

• Add Usage prefix pattern to classifier ("usage of X", "uses of X")
• Add understandingPattern for "how does X work" queries
• Implement handleUsage with kb_index lookup and source extraction
• Implement handleMetrics from kb_metrics.json (project summary + top 10)
• Implement handleEntryPoints from kb_entry_points.json
• Implement buildRouterCallGraph from CallGraphRef edges
• Add bareID normalization for node type prefixes (func_, method_, type_)
• Add parseLocation, extractSignature for file+line source extraction
• Add dedupe helper for kb_index deduplication
• Add stripCommandPrefix for cleaner entity extraction
• Replace KBIndex with types.KBIndices across codebase
• Add debug logging for each handler and router path

Version: v0.7.0