Add provider fallback, visual schema builder, and UI improvements

Provider fallback system:
- Add optional fallback field to Provider dataclass
- Automatically try fallback provider when primary fails (timeout, error, offline)
- Prevent infinite loops with circular fallback detection
- Add fallback column and dropdown in providers UI

Visual schema builder for prompt steps:
- Add SchemaBuilderDialog with table-based field editor
- Support field name, type, description, and required flag
- Live JSON schema preview
- Integrate into PromptStepDialog with Edit Schema button
- Fix output_schema being lost when editing prompt steps

Other improvements:
- Add search box to tools page
- Improve schema example generation for structured output
- Update CLAUDE.md documentation

Co-Authored-By: Claude Opus 4.5 <[email protected]>

CLAUDE.md

@@ -15,14 +15,12 @@ pip install -e ".[dev]"
 # Run all unit tests (excluding integration tests that need a server)
 pytest tests/ -m "not integration"
 
-# Run all tests with verbose output
-pytest tests/ -v
-
 # Run a specific test file
 pytest tests/test_runner.py -v
 
-# Run a specific test class
+# Run a specific test class or method
 pytest tests/test_runner.py::TestSubstituteVariables -v
+pytest tests/test_runner.py::TestSubstituteVariables::test_simple_substitution -v
 
 # Run with coverage
 pytest tests/ --cov=cmdforge --cov-report=html
@@ -31,11 +29,10 @@ pytest tests/ --cov=cmdforge --cov-report=html
 python -m cmdforge.registry.app  # Start server first
 pytest tests/test_registry_integration.py -v -m integration
 
-# Run the CLI
-python -m cmdforge.cli
-
-# Launch the GUI
-cmdforge
+# CLI entry points
+cmdforge              # Main CLI / GUI launcher
+cf                    # Interactive tool picker (fzf-style)
+python -m cmdforge.cli  # Alternative CLI invocation
 ```
 
 ## Architecture
@@ -76,7 +73,10 @@ Tools are YAML configs with:
 
 ### Step Types
 
-1. **Prompt Step**: Calls AI provider with template, stores result in `output_var`. Supports `profile` for AI personas and `strip_fences` for markdown cleanup
+1. **Prompt Step**: Calls AI provider with template, stores result in `output_var`
+   - `profile`: AI persona (system prompt prefix)
+   - `strip_fences`: Remove markdown code fences from output
+   - `structured_output`: JSON schema for validated structured responses
 2. **Code Step**: Executes Python code via `exec()`, captures specified variables (comma-separated for multiple outputs)
 3. **Tool Step**: Calls another tool (meta-tools), supports `args` dict and `provider` override. Dependencies resolved via `resolver.py`
 
@@ -103,7 +103,7 @@ providers:
     command: "echo '[MOCK]'"
 ```
 
-The `mock` provider is built-in for testing without API calls.
+The `mock` provider is built-in for testing without API calls. Use `--provider mock` or `--dry-run` flags when testing tools.
 
 ## Web UI & Registry
 
@@ -145,14 +145,22 @@ CMDFORGE_REGISTRY_DB=/path/to/db PORT=5050 python -m cmdforge.web.app
 
 ## Testing Conventions
 
-Tests use `pytest` with common fixtures:
-- `temp_tools_dir(tmp_path)`: Redirects `TOOLS_DIR` and `BIN_DIR` to temp directory
-- `temp_providers_file(tmp_path)`: Redirects `providers.yaml` to temp directory
+Tests use `pytest` without a shared conftest.py. Common patterns:
 
-Mocking strategy:
-- **File system**: Use `tmp_path` fixture and patch module-level paths
+**Mocking strategy:**
+- **File system**: Use `tmp_path` fixture and patch module-level paths (`TOOLS_DIR`, `BIN_DIR`, `PROVIDERS_FILE`)
 - **Subprocess calls**: Mock `subprocess.run` and `shutil.which`
-- **Provider calls**: Mock `call_provider` to return `ProviderResult`
+- **Provider calls**: Mock `call_provider` to return `ProviderResult(text="...", success=True)`
+- **Registry calls**: Mock `requests` for API tests
+
+**Example fixture pattern:**
+```python
+@pytest.fixture
+def temp_providers_file(tmp_path):
+    providers_file = tmp_path / "providers.yaml"
+    with patch('cmdforge.providers.PROVIDERS_FILE', providers_file):
+        yield providers_file
+```
 
 Integration tests are marked with `@pytest.mark.integration` and require a running registry server.