refactor: reorganize into monorepo with separate subprojects

Structure webber into three independent subprojects:
- webber-api/: FastAPI backend server with all agent code
- webber-cli/: Standalone CLI client (renamed from cli/ to webber_cli/)
- webber-sandbox/: Test project for functional testing

Key changes:
- Each subproject has its own .venv (Python 3.12+)
- Added sandbox.sh for managing test project templates
- Created sandbox-templates/ with calculator-cli and empty starter
- Updated CI/CD for prefixed tags (api/v*, cli/v*)
- Added comprehensive AGENTS.md with operational instructions
- Added gitignore filtering to glob and grep tools
- Created pyproject.toml for each subproject

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

webber-api/requirements-dev.txt

@@ -0,0 +1,20 @@
+# Webber Development Dependencies
+# Install with: pip install -r requirements-dev.txt
+# NOT included in production Docker image
+# CVE check date: 2026-01-09
+
+-r requirements.txt
+
+# Testing
+pytest~=9.0.2
+anyio~=4.12.1                          # Includes pytest-anyio plugin
+pytest-cov~=7.0.0
+
+# Security auditing - run before releases: pip-audit
+pip-audit~=2.9.0
+
+# Type checking
+mypy~=1.19.1
+
+# Linting and formatting
+ruff~=0.9.4