Keep redrawn progress rows in place instead of repeating them

[graeme]

PR: Fix console progress repeating on multi-package operations

Summary

The console redrew Homebrew's parallel download block on every tick instead of updating it in place, so a multi-package operation filled the pane with duplicated rows. Reported with a screenshot showing the cask list repeated at different byte counts.

Changes

Homebrew's download queue draws N rows, leaves the last without a trailing newline, then rewinds with ESC[<n>F (cursor previous line) to draw the next frame over the top. TerminalLineAssembler handled SGR, ESC[K and the column moves but dropped everything else, so the rewind was lost. That gap caused both symptoms: the block repeated, and the last row spliced into the next frame's first row.

• TerminalLineAssembler keeps a window of committed rows addressable, sized to the pty's row count, and handles ESC[F, ESC[A and ESC[B. Inside a block, a newline steps the cursor down a row rather than opening one. Movement above the window is ignored rather than writing to a wrong row.
• TerminalLineEvent.revised carries a row offset. BrewCommandOutputLine and CommandJob.appendOutput route by it, counting back from the end so offsets stay valid after maxOutputLines trims the front.
• BrewCommandService builds the returned transcript from settled rows rather than every frame.

Testing

• scripts/test: 780 package tests plus 19 BrewUILint tests
• 31 new tests: both symptoms, cursor semantics, offset arithmetic, window boundary
• Integration test driving a real zsh subprocess through the pty
• swiftformat, swiftlint --strict, BrewUILint, xcodebuild -scheme Brew
• Manual: brew install node at concurrency 8, on main and on this branch

PR checklist

• Have you followed this repository's contribution and workflow guidance?
• Have you explained what changed and why this should land now?
• Have you run relevant local checks for the changed scope?
• Are changes scoped and free of unrelated modifications?

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• AI was used to generate or assist with generating this PR.
• AI traced the missing CPL handling against download_queue.rb and wrote the implementation, tests and this description. Verified manually by reproducing the block on main and confirming one row per download here.

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Follow-ups

• The pty is fixed at 120x40, so brew formats columns for 120 regardless of console width.
• Absolute positioning, erase-in-display, scroll regions and the alternate screen still need a real screen buffer.