codegraph_explore now reads code internally (sub-agent behavior)

Instead of returning file paths for Claude to read separately,
codegraph_explore now:
- Reads relevant files internally using fs
- Extracts code snippets for key symbols (functions, types, APIs)
- Includes the code directly in the response
- Returns a synthesis with data flow and key code included

This matches native explore agent behavior where file reading
happens in the sub-agent context, keeping main context clean.

Bump version to 0.1.8

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@colbymchenry/codegraph",
-  "version": "0.1.7",
+  "version": "0.1.8",
   "description": "A local-first code intelligence system that builds a semantic knowledge graph from any codebase",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",