docs(issue): update agent/prompts to use CLI endpoints

- issue-plan-agent.md: Use `ccw issue solution` instead of Bash echo
- issue-plan.md (codex): Use `ccw issue solution` endpoint
- issue-queue.md (codex): Remove assigned_executor from schema

All solution creation now uses the dedicated CLI endpoint for:
- Auto-increment ID: SOL-{issue-id}-{seq}
- Proper JSONL format with trailing newline
- Multi-solution support per issue

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.codex/prompts/issue-queue.md

@@ -135,7 +135,6 @@ Group assignment:
       "execution_group": "P1",
       "depends_on": [],
       "semantic_priority": 0.8,
-      "assigned_executor": "codex",
       "files_touched": ["src/auth.ts"],
       "task_count": 3
     }