feat: add research agent for analyzing existing codebases

Complete workflow for onboarding existing projects to AutoForge:

Backend:
- Research MCP server with 6 tools for codebase analysis
- Technology stack detection (70+ frameworks)
- Architecture pattern analysis and code convention extraction
- Research state persistence via SQLAlchemy
- Git branch safety (protected branch warnings, branch creation)
- Auto-delete CLAUDE.md after spec creation to prevent agent confusion
- REST endpoints for research agent lifecycle (start/stop/status)

Frontend:
- Analyze Codebase modal with folder browser integration
- Research progress view with real-time WebSocket updates
- Research results viewer with tabbed markdown display
- Branch selection modal for safe git operations
- Re-analyze Codebase button for updating documentation
- Reinitialize Features modal for research-to-spec flow

Workflow:
1. Click "Analyze Existing Codebase" and select project folder
2. Research agent generates documentation in .planning/codebase/
3. Review results and convert to app spec
4. Choose git branch for safe development
5. Continue with normal AutoForge agent workflow

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: maswa

.claude/commands/gsd-map-codebase.md

@@ -0,0 +1,10 @@
+---
+allowed-tools: Read, Glob, Grep, Bash, mcp__research__*
+description: Analyze existing codebase and document structure
+---
+
+# Map Existing Codebase
+
+Analyze an existing codebase and generate documentation for use with AutoForge.
+
+@.claude/templates/research_prompt.template.md