📝 docs: add CacheManager pattern documentation and usage guidelines

| CLI command | `src/tdoc_crawler/cli/tdoc_app.py` | Typer app, Rich console |

| Pydantic model | `src/tdoc_crawler/models/` | Data validation, serialization |

| HTTP caching | `src/tdoc_crawler/http_client.py` | `create_cached_session()` |

| Path management | `src/tdoc_crawler/config/__init__.py` | `CacheManager`, `resolve_cache_manager()` |

| Test structure | `tests/test_crawler.py` | Fixtures, mocking, isolation |

## Heuristics (quick decisions)

| When | Do |

|------|-----|

| Adding HTTP request | Use `create_cached_session()` |

| Need file/directory paths | Use `CacheManager` (NEVER hardcode `~/.3gpp-crawler`) |

| Unsure import path | Check scoped AGENTS.md for domain |

| Circular import detected | Extract shared types to `models/` |

| Adding dependency | Ask first - minimize deps |

- Commit `.env` files

- Run `git commit` or `git push` autonomously

- Duplicate code (search first, refactor if needed)

- **Hardcode paths** like `~/.3gpp-crawler` - always use `CacheManager`

- **Define duplicate path constants** - check `src/tdoc_crawler/config/__init__.py` first

## Terminology

| TSG | Technical Specification Group (SA, RAN, CT) |

| Portal | 3GPP EOL authenticated portal |

## CacheManager Pattern (CRITICAL)

**Single Source of Truth:** All file paths MUST use `CacheManager` from `src/tdoc_crawler/config/__init__.py`.

### Usage

```python

from tdoc_crawler.config import resolve_cache_manager, CacheManager

# Get registered manager (preferred)

manager = resolve_cache_manager()

# Or create new (auto-registers)

manager = CacheManager().register()

# Access paths (NEVER hardcode these)

manager.root              # ~/.3gpp-crawler/

manager.db_file           # ~/.3gpp-crawler/3gpp_crawler.db

manager.http_cache_file   # ~/.3gpp-crawler/http-cache.sqlite3

manager.checkout_dir      # ~/.3gpp-crawler/checkout/

manager.ai_cache_dir      # ~/.3gpp-crawler/lightrag/

manager.ai_workspace_file # ~/.3gpp-crawler/lightrag/workspaces.json

manager.ai_embed_dir(model)  # ~/.3gpp-crawler/lightrag/{model}/

```

### Why This Matters

- **DRY principle:** Path logic defined once, used everywhere

- **Configurability:** Users can override via `TDC_CACHE_DIR` and `TDC_AI_STORE_PATH` env vars

- **Consistency:** All components use identical paths

- **Testability:** Easy to swap in test directories

### Common Mistakes to Avoid

```python

# ❌ WRONG - Never hardcode paths

Path.home() / ".3gpp-crawler" / "lightrag"

os.path.expanduser("~/.3gpp-crawler")

# ✅ CORRECT - Always use CacheManager

manager = resolve_cache_manager()

manager.ai_cache_dir

manager.ai_embed_dir("qwen3-embedding-0.6b")

```

## Scoped AGENTS.md (MUST read when working in these directories)

| Directory | Purpose |