fix(read): window tracking baseline

[wyf027]

Summary

• Fixes rtk read: truncation via --max-lines incorrectly counted as token savings, producing 250M+ saved tokens in one command #1045.
• Apply the same --max-lines / --tail-lines window to the raw tracking baseline that is applied to filtered output.
• This prevents content dropped by the window from being counted as token savings while preserving real filter savings inside the visible window.
• Add focused tests for max-lines and tail-lines baseline behavior.

Test plan

• cargo fmt --all --check
• cargo test prepare_outputs -- --nocapture
• cargo test apply_line_window -- --nocapture
• git diff --check
• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk read --max-lines 2 <file> output inspected

[CLAassistant]

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