Add Qwen Code support to convert.sh and install.sh

- Add convert_qwen() to scripts/convert.sh for generating Qwen SubAgent .md files
- Add install_qwen() to scripts/install.sh for installing to .qwen/agents/ (project-scoped)
- Add qwen detection, tool label, and install cases
- Update README.md with Qwen in supported tools table + usage section
- Add integrations/qwen/agents/ to .gitignore + create .gitkeep
- Add Qwen Code compatibility note to CONTRIBUTING.md
- Preserve tools: field in Qwen output when present in source agents
- Fix interactive installer to show dynamic [1-N] toggle range
- Update README roadmap checklist to include Qwen Code

Qwen SubAgents use minimal YAML frontmatter (name, description) with optional tools: field preserved from source. Body content passes through unchanged.
Tested with 120 agents — all convert and install successfully.

CONTRIBUTING.md

@@ -214,6 +214,10 @@ The test: *is this agent for the user, or for the vendor?* An agent that
 solves the user's problem using a service belongs here. A service's
 quickstart guide wearing an agent costume does not.
 
+### Tool-Specific Compatibility
+
+**Qwen Code Compatibility**: Agent bodies support `${variable}` templating for dynamic context (e.g., `${project_name}`, `${task_description}`). Qwen SubAgents use minimal frontmatter: only `name` and `description` are required; `color`, `emoji`, and `version` fields are omitted as Qwen doesn't use them.
+
 ### What Makes a Great Agent?
 
 **Great agents have**: