docs: annotate generic Context examples #427

Problem

PR #414 added strict typing coverage for the examples and compatibility consumers, but the public snippets in README.md and docs/integrations.md still annotate callbacks as base_cli.Context without its three required type parameters. Strict mypy rejects that form as a missing generic type argument.

Scope

Update the affected public examples to use an explicit, neutral base_cli.Context[object, object, object] annotation (or an equivalent documented alias). Keep the examples readable and do not change the public API or runtime behavior.

Acceptance criteria

• No public README or integration example uses unparameterized base_cli.Context.
• The affected snippets remain consistent with docs/user-config-typing.md and the three-parameter public Context contract.
• Documentation validation and the strict typing gate pass.

Origin

Follow-up to merged PR #414 / issue #393 review feedback.