Fix grammar and improve text readability (#81)

* Fix grammar

* Add FastAPI best practices skill

* Add CLAUDE.md with FastAPI best practices

* Add more tips to CLAUDE.md

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Co-authored-by: Claude <noreply@anthropic.com>

CLAUDE.md

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+# FastAPI Best Practices
+
+## Project Structure
+Organize by domain (`src/auth/`, `src/posts/`), not file type. Each domain has: `router.py`, `schemas.py`, `models.py`, `service.py`, `dependencies.py`, `config.py`, `exceptions.py`.
+
+## Async Routes
+- `async def` → non-blocking I/O only
+- `def` (sync) → blocking operations (runs in threadpool)
+- CPU-intensive → offload to worker processes (Celery, multiprocessing)
+- Sync SDK? Use `run_in_threadpool` from Starlette
+
+## Pydantic
+- Use extensively: regex, enums, Field constraints, EmailStr
+- Split BaseSettings per domain
+- Create custom base model for app-wide serialization
+- ValueError in schema → returns ValidationError to client
+
+## Dependencies
+- Use for DB/service validations, not just DI
+- Chain dependencies to avoid repetition
+- Prefer `async` dependencies
+- Dependencies are cached per request
+
+## Follow the REST
+- Consistent path variable names enable dependency reuse
+- `/profiles/{profile_id}` and `/creators/{profile_id}` can share `valid_profile_id` dependency
+
+## Database
+- Explicit naming conventions for indexes/constraints
+- `lower_case_snake`, singular table names
+- SQL-first for joins and aggregations
+- Aggregate nested JSON in DB, not Python
+
+## Migrations (Alembic)
+- Keep migrations static and reversible
+- Use descriptive slugs: `2022-08-24_post_content_idx.py`
+
+## Testing
+- Async test client from day 0 (httpx)