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-cli/README.md

@@ -0,0 +1,42 @@
+# Webber CLI
+
+Command-line client for the Webber API.
+
+## Installation
+
+```bash
+# Create virtual environment
+python3.12 -m venv .venv
+source .venv/bin/activate
+
+# Install dependencies
+pip install -r requirements.txt
+
+# Install package in editable mode
+pip install -e .
+```
+
+## Usage
+
+```bash
+# Check API connection
+webber-cli status
+
+# Explore a codebase
+webber-cli explore "find all python files" -d /path/to/project
+
+# Interactive chat mode
+webber-cli chat -d /path/to/project
+```
+
+## Configuration
+
+Set the API URL via environment variable:
+```bash
+export WEBBER_API_URL=http://localhost:8095
+```
+
+## Requirements
+
+- Python 3.12+
+- Webber API running (see `../webber-api/`)