feat(cli): detect terminal theme via OSC 11

[emal-avala]

Summary

• Add CLI-only OSC 11 background detection with a DA1 sentinel, BT.709 luminance classification, TTY gating, a 1s timeout, and inherited env override support.
• Route auto theme resolution through the cached terminal query while preserving the existing theme palette implementation.
• Cover OSC parser variants, malformed replies, luminance boundaries, and simulated query I/O.

Test plan

• cargo check --all-targets (GitHub Actions CI run 943)
• cargo test --all-targets (GitHub Actions CI run 943, Ubuntu + Windows)
• cargo clippy --all-targets -- -D warnings (GitHub Actions CI run 943)
• cargo fmt --all -- --check (GitHub Actions CI run 943)
• Added parser/luminance/simulated-I/O test coverage for the new terminal query module

Local cargo commands were not run because the local sandbox wrapper fails before shell startup.

[chatgpt-codex-connector]

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