Add meta-tools, collections, and attribution features

Meta-tools:
- Add ToolStep dataclass for tools calling other tools
- Implement execute_tool_step() with recursion depth limiting
- Add check_dependencies() for validating tool dependencies
- Add 'cmdforge check' command for dependency verification

Collections:
- Add collections API endpoints and database schema
- Create collections web UI (list and detail pages)
- Add collections to navigation header and homepage
- Document collections in REGISTRY.md

Attribution:
- Add source attribution fields to tool detail page
- Document source types (original, adapted, imported)
- Add license field documentation

Documentation updates across README, DESIGN.md, REGISTRY.md,
and new META_TOOLS.md design document.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

README.md

@@ -26,6 +26,7 @@ echo "Price $49.99, SKU ABC-123" | json-extract --fields "price, sku"
 - **Provider Agnostic** - Works with Claude, GPT, Gemini, DeepSeek, local models
 - **No Lock-in** - Your tools are YAML files, your prompts are yours
 - **Multi-step Pipelines** - Chain AI prompts with Python code for validation
+- **Meta-tools** - Tools can call other tools for powerful composition
 - **12+ Providers Profiled** - We tested them so you don't have to
 
 ## Try It Now (60 seconds)
@@ -129,6 +130,7 @@ cmdforge edit mytool       # Edit in $EDITOR
 cmdforge delete mytool     # Delete tool
 cmdforge run mytool        # Run a tool
 cmdforge test mytool       # Test with mock provider
+cmdforge check mytool      # Check dependencies (meta-tools)
 cmdforge refresh           # Update executable wrappers
 ```
 
@@ -340,13 +342,44 @@ steps:
 output: "{validated}"
 ```
 
+### Meta-Tools (Tools Calling Tools)
+
+Tools can call other tools as steps, enabling powerful composition:
+
+```yaml
+name: summarize-and-translate
+description: Summarize text then translate the summary
+dependencies:
+  - official/summarize
+  - official/translate
+steps:
+  - type: tool
+    tool: official/summarize
+    input: "{input}"
+    args:
+      max_words: "100"
+    output_var: summary
+
+  - type: tool
+    tool: official/translate
+    input: "{summary}"
+    args:
+      target_language: "{language}"
+    output_var: translated
+output: "{translated}"
+```
+
+Check dependencies before running: `cmdforge check my-meta-tool`
+
+See [docs/META_TOOLS.md](docs/META_TOOLS.md) for full documentation.
+
 ### Variables
 
 | Variable | Description |
 |----------|-------------|
 | `{input}` | The piped/file input |
 | `{argname}` | Custom argument value |
-| `{step_output}` | Output from previous step |
+| `{output_var}` | Output from previous step (prompt, code, or tool) |
 
 ## Shell Integration
 
@@ -563,6 +596,7 @@ cmdforge providers test claude
 ### Developer Documentation
 - [Project Overview](docs/PROJECT.md) - Start here to understand the codebase
 - [Design Document](docs/DESIGN.md)
+- [Meta-Tools Design](docs/META_TOOLS.md) - Tools that call other tools
 - [Registry API Design](docs/REGISTRY.md)
 - [Web UI Design](docs/WEB_UI.md)
 - [Deployment Guide](docs/DEPLOYMENT.md)