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>

.gitea/workflows/build-cli.yml

@@ -0,0 +1,25 @@
+name: Build and Release CLI
+
+on:
+  push:
+    tags:
+      - 'cli/v*'
+
+# TODO: Implement CLI installer build
+# This workflow will be implemented when CLI distribution is ready.
+# Possible targets:
+# - PyPI package
+# - Standalone binary (PyInstaller)
+# - Platform-specific installers
+
+jobs:
+  placeholder:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Extract version from tag
+        id: version
+        run: |
+          VERSION="${{ github.ref_name }}"
+          VERSION="${VERSION#cli/}"
+          echo "CLI release triggered for version: $VERSION"
+          echo "TODO: Implement CLI build and distribution"