refactor: Standardize agent references to @agent-name format

- Convert direct agent name references to @agent-name format in documentation
- Preserve Task() function calls and subagent_type parameters unchanged
- Keep task content agent identifiers in original format (for display only)
- Maintain document reference paths in original format
- Update workflow architecture, task management, and execution files

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

Co-Authored-By: Claude <noreply@anthropic.com>

.claude/commands/workflow/execute.md

@@ -233,10 +233,10 @@ Task(subagent_type="{agent_type}",
 ```
 meta.agent specified → Use specified agent
 meta.agent missing → Infer from meta.type:
-  - "feature" → code-developer
-  - "test" → code-review-test-agent
-  - "review" → code-review-agent
-  - "docs" → doc-generator
+  - "feature" → @code-developer
+  - "test" → @code-review-test-agent
+  - "review" → @code-review-agent
+  - "docs" → @doc-generator
 ```
 
 #### Error Handling During Execution