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/calculator-cli/src/calculator/operations.py

@@ -0,0 +1,43 @@
+"""
+Math operations for the calculator.
+
+NOTE: This file contains intentional bugs for testing purposes.
+"""
+
+
+def add(a: float, b: float) -> float:
+    """Add two numbers."""
+    return a + b
+
+
+def subtract(a: float, b: float) -> float:
+    """Subtract b from a."""
+    return a - b
+
+
+def multiply(a: float, b: float) -> float:
+    """Multiply two numbers."""
+    return a * b
+
+
+def divide(a: float, b: float) -> float:
+    """
+    Divide a by b.
+
+    BUG: Does not handle division by zero!
+    """
+    # BUG: No check for b == 0
+    return a / b
+
+
+def power(a: float, b: float) -> float:
+    """
+    Raise a to the power of b.
+
+    BUG: Negative exponents not handled correctly for some cases.
+    """
+    # BUG: This naive implementation has issues with negative bases and fractional exponents
+    result = 1
+    for _ in range(int(b)):
+        result *= a
+    return result