docs: rename general-purpose agent to universal-executor and update documentation

Major updates in this release:

1. Agent Renaming (13 files, 21 references):
   - Renamed general-purpose → universal-executor to avoid naming conflicts
   - Updated all references in commands and workflows
   - Maintained backward compatibility in documentation

2. README Updates (4 files):
   - Removed /workflow:session:start step (auto-created by /workflow:plan)
   - Simplified workflow from 4 steps to 3 steps
   - Updated version to v4.6.2
   - Added CLI tool usage guidelines

3. GETTING_STARTED Enhancements (2 files):
   - Added Design Philosophy section explaining multi-model CLI integration
   - Added comprehensive CLI tool usage guide with common workflows
   - Reorganized quick start to emphasize automatic session creation
   - Added examples for bug fixes and feature development

Files modified:
- Agent config: .claude/agents/general-purpose.md
- Commands: 7 files in .claude/commands/
- Workflows: 5 files in .claude/workflows/
- Documentation: README.md, README_CN.md, GETTING_STARTED.md, GETTING_STARTED_CN.md

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

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

.claude/commands/workflow/tools/task-generate.md

@@ -174,7 +174,7 @@ This enhanced 5-field schema embeds all necessary context, artifacts, and execut
   "status": "pending|active|completed|blocked|container",
   "meta": {
     "type": "feature|bugfix|refactor|test-gen|test-fix|docs",
-    "agent": "@code-developer|@test-fix-agent|@general-purpose",
+    "agent": "@code-developer|@test-fix-agent|@universal-executor",
     "execution_group": "group-id|null",
     "context_signature": "hash-of-focus_paths-and-artifacts"
   },