fix(codemode): preserve block tint across truncated rows

[outlier27-cell]

Fixes #683

Preserve the Code Mode block background/tint when a long tool result is truncated into additional rows, so the continuation remains visually associated with the original block.

Validation:

• targeted Code Mode tests: 14/14
• format, lint, typecheck, diff check

[outlier27-cell]

Fixed the CI regression in 9fd3153: the tint helper now preserves native ANSI reset markers while reopening the block background after each reset. Targeted codemode suite: 21/21; bun run check: passed. Exact-head GitHub CI is now green across Node, Windows, UI, and E2E.

[outlier27-cell]

@tt-a1i 请审核此 PR。最新提交已通过完整 GitHub CI，当前可合并；如有需要调整的地方，我会在原分支及时修复。

[outlier27-cell]

@tt-a1i 已更新至最新 main，最新提交的完整 CI 已通过，烦请审核。

[outlier27-cell]

@testikun @tt-a1i 请审核此 PR。最新提交的 CI 已通过，当前仅等待维护者审核与合并。

[outlier27-cell]

@testikun @tt-a1i 请审核此 PR。最新提交的 CI 已通过，当前仅等待维护者审核与合并。

[tt-a1i]

Exact reviewed head: a9eb64c4430a2f8eb34fc52b6207c0eb2a59285c.

Current main already includes the CodeMode background-fill production fix via #684. Green CI does not create independent merge value for duplicate production code. Verify equivalence, preserve any unique missing regression, and propose closing this superseded PR. Closure remains a maintainer decision.

Verification: prior exact-head Standards and Spec evidence reused because this head is unchanged; current review/CI/integration metadata refreshed. No complete-suite rerun, installed-runtime/provider run, or visual acceptance performed in this update.

[outlier27-cell]

已按评论逐项对比 #684 与 #691：#684 已合入同一生产修复，并已有多宽度、折叠/展开、ANSI reset、ellipsis 与右侧填充的完整回归。#691 的新增断言不再提供独有覆盖价值。请维护者按建议关闭 #691，避免保留重复的生产改动。

[tt-a1i]

It looks like main already reapplies the block background after each ESC[0m (extensions/codemode-display/render.ts), so against current main this PR reduces to a refactor plus a test that already passes there. Unless the test covers a case main still gets wrong, I'd close this and #683 as already fixed. Thanks for the report!