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-sandbox/TASKS.md

@@ -0,0 +1,64 @@
+# Calculator CLI - Tasks for Webber
+
+A simple calculator with intentional bugs and missing features for testing Webber's capabilities.
+
+## Bugs to Fix
+
+### High Priority
+- [ ] **Division by zero** - `operations.py:divide()` crashes when dividing by zero instead of returning an error
+- [ ] **Invalid operation name** - `main.py:get_operation()` raises KeyError for unknown operations instead of helpful error message
+
+### Medium Priority
+- [ ] **Power function broken** - `operations.py:power()` doesn't handle negative exponents or fractional exponents correctly
+- [ ] **No input validation** - `main.py` doesn't validate that command-line arguments are valid numbers
+
+## Missing Tests
+
+- [ ] Add `TestDivide` class with tests for:
+  - Normal division
+  - Division by zero (should test error handling once bug is fixed)
+  - Division with negative numbers
+
+- [ ] Add `TestPower` class with tests for:
+  - Positive integer exponents
+  - Zero exponent (should return 1)
+  - Negative exponents
+
+- [ ] Complete existing test classes:
+  - `test_add_zero`
+  - `test_add_floats`
+  - `test_subtract_negative`
+  - `test_multiply_by_zero`
+
+## Features to Add
+
+- [ ] **Expose power operation** - Add 'pow' to the operations dictionary in `main.py`
+- [ ] **Add modulo operation** - Implement `modulo(a, b)` in operations.py
+- [ ] **Add --verbose flag** - Show step-by-step calculation
+- [ ] **Add history command** - Track and display recent calculations
+- [ ] **Add REPL mode** - Interactive calculator loop
+
+## Code Quality
+
+- [ ] Add type hints to all functions
+- [ ] Add docstrings following Google style
+- [ ] Fix any linting errors (run `ruff check src/`)
+
+## How to Run
+
+```bash
+# Setup
+python3.12 -m venv .venv
+source .venv/bin/activate
+pip install -r requirements.txt
+
+# Run calculator
+python -m calculator.main 10 5 add
+python -m calculator.main 10 5 div
+
+# Run tests
+pytest tests/ -v
+
+# See failing tests (division by zero)
+python -m calculator.main 10 0 div
+```