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>

sandbox-templates/empty/.gitignore

@@ -0,0 +1,25 @@
+# Python
+__pycache__/
+*.py[cod]
+*.so
+.Python
+build/
+dist/
+*.egg-info/
+
+# Virtual environments
+.venv/
+venv/
+
+# Testing
+.pytest_cache/
+.coverage
+htmlcov/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+
+# Project
+.current_template

sandbox-templates/empty/TASKS.md

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+# My Project - Tasks
+
+A blank starter template. Define your own tasks here.
+
+## Setup
+
+```bash
+python3.12 -m venv .venv
+source .venv/bin/activate
+pip install -r requirements.txt
+```
+
+## Tasks
+
+- [ ] Define your project goals
+- [ ] Add source files to `src/myproject/`
+- [ ] Add tests to `tests/`
+- [ ] Update `requirements.txt` with dependencies

sandbox-templates/empty/pyproject.toml

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+[project]
+name = "myproject"
+version = "0.1.0"
+description = "A blank starter project"
+requires-python = ">=3.12"
+
+[build-system]
+requires = ["setuptools>=75.0"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+pythonpath = ["src"]
+addopts = "-v"

sandbox-templates/empty/requirements.txt

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+# Add your dependencies here
+pytest>=8.0.0

sandbox-templates/empty/src/myproject/__init__.py

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+"""My Project - A blank starter template."""
+
+__version__ = "0.1.0"

sandbox-templates/empty/tests/__init__.py

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+"""Tests for myproject."""