Explore + GitHub Adapters

[prosdev]

Description

Add code exploration and GitHub context tools. Completes core adapter set.

Milestone: All core functionality exposed via MCP! ✅

Scope

• ExploreAdapter (dev_explore tool: pattern, similar, relationships)
• GitHubAdapter (dev_gh tool: search, context, related)
• Unit tests for both
• Integration tests

Acceptance Criteria

• dev_explore supports pattern, similar, relationships
• dev_gh supports search, context, related
• Both adapters token-efficient
• >80% test coverage
• All dev-agent features accessible via MCP

Estimate: 2 days
Parent Epic: #26 (MCP Integration)
Depends on: #29