Document session, sales-channel context, and cart lifecycles with clear config boundaries

[Copilot]

The docs did not explain how Symfony session lifetime, Store API context lifetime, persisted sales-channel context, and cart expiration interact, which made login/cart persistence behavior hard to reason about. This update adds a single, centralized explanation that separates each lifecycle and its controlling config.

• Added lifecycle overview in guides/hosting/performance/session.md

  • New section: Session, context, and cart lifetime
  • Clarifies that these lifecycles are independent and can expire at different times.

• Added UML sequence diagram (Mermaid)

  • Visualizes flow across browser session cookie, Symfony session, sales-channel context token, and cart token.

• Added config-to-behavior comparison table

  • Distinguishes each setting by scope, token/data affected, and expiration effect:
    • framework.session.cookie_lifetime
    • framework.session.gc_maxlifetime
    • shopware.api.store.context_lifetime
    • shopware.sales_channel_context.expire_days
    • shopware.cart.expire_days

• Added concise risk/capacity guidance

  • Notes security tradeoffs of longer lifetimes on shared devices.
  • Notes infrastructure impact (e.g., higher Redis memory usage) for longer retention windows.

sequenceDiagram
    participant Browser
    participant Symfony Session
    participant Sales Channel Context
    participant Cart
    Browser->>Symfony Session: Store session cookie
    Symfony Session->>Sales Channel Context: Resolve context token
    Sales Channel Context->>Cart: Load cart by token

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