feat: restore AppError::with_context helper

[RAprogramm]

Summary

• add AppError::with_context helper that reuses Arc sources and update Context builder to call it
• document the helper across lib docs, README, and wiki content and add regression tests for plain and anyhow errors
• bump crate version to 0.23.1 and record the change in the changelog

Testing

• cargo +nightly fmt --
• cargo +1.90.0 clippy -- -D warnings
• cargo +1.90.0 build --all-targets
• cargo +1.90.0 test --all
• cargo +1.90.0 doc --no-deps
• cargo audit
• cargo deny check

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https://chatgpt.com/codex/tasks/task_e_68d64a3e20a4832ba4dbb8e1bf480329