fix: wire cbm_store_get_architecture into handle_get_architecture MCP handler

[Copilot]

get_architecture only ever returned label/type histograms (node_labels, edge_types, relationship_patterns) because handle_get_architecture never called cbm_store_get_architecture — the rich architecture computation layer was completely bypassed regardless of which aspects were requested.

Changes

• Extract aspects for store dispatch — parse the JSON aspects array into a const char*[] and pass it to cbm_store_get_architecture, which already handles "all" and per-name filtering internally
• Serialize all populated architecture sections — after calling the store, emit each non-empty field from cbm_architecture_info_t:
  • languages (language, file_count)
  • packages (name, node_count, fan_in, fan_out)
  • entry_points (name, qualified_name, file)
  • routes (method, path, handler)
  • hotspots (name, qualified_name, fan_in)
  • boundaries (from, to, call_count)
  • layers (name, layer, reason)
  • file_tree (path, type, children)
• Preserve existing histogram fields — node_labels, edge_types, relationship_patterns, and cross_repo_links are unchanged
• Proper cleanup — cbm_store_architecture_free called before return