Add Tortoise ORM Agents Skill

[waketzheng]

Summary

Add a Tortoise ORM Claude skill under .claude/skills/tortoise-orm/SKILL.md.

The skill documents repository-specific guidance for AI coding assistants, including:

• uv/Makefile development commands
• project layout and API design priorities
• async ORM conventions
• model, field, queryset, backend, migration, and integration guidance
• testing and documentation expectations
• compatibility notes and common pitfalls

This follows the same general idea as FastAPI's Agents Skill added in fastapi/fastapi#14982, adapted for Tortoise ORM's codebase and workflow.

Tests

• git diff --check

No runtime tests were run because this only adds Claude/agent guidance documentation.

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

---

_{Comparing waketzheng:ai-skill (058a77b) with develop (179ea6f)}