feat: store shared sources and lazy backtraces

[RAprogramm]

Summary

• store AppError sources behind shared Arc handles and capture optional backtraces lazily under the backtrace feature with RUST_BACKTRACE
• wire the derive and ResultExt conversions through the new storage so source chains and backtrace snapshots are preserved automatically
• bump the workspace crates to 0.19.0/0.9.0 and document the behaviour in the changelog and README

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_68d337593bf8832b8a92921925dc7d73