fix: add circular dependency detection at build time

[hartym]

Summary

• Add circular dependency detection during ContainerBuilder.build() using DFS
• Raises CircularDependencyError with full cycle path (e.g., "A → B → C → A")
• Fix documentation to use correct async API (await, async with)
• Add documentation for lifecycle hooks and autowire parameter

Fixes #1

Changes

Circular Dependency Detection

• Implement DFS-based cycle detection in _check_circular_dependencies()
• Detect direct cycles (A → B → A), indirect cycles (A → B → C → A), and self-references
• Correctly allow diamond patterns (shared dependencies)
• Works regardless of scope configuration (singleton, scoped, transient)

Documentation Fixes

• Add pre-alpha warning to documentation index
• Fix all code examples to use await container.get() and async with container.scope()
• Document initializer, finalizer, and autowire parameters
• Remove references to non-existent exceptions
• Fix toctree order to follow Diátaxis framework

Test Plan

• All 113 tests pass
• New tests for cycle detection (direct, indirect, self-reference, diamond pattern)
• Documentation builds without errors
• Linting and type checking pass