fix(shell): prevent Rich default markdown styles from leaking background colors

[RealKai42]

Summary

• Override all Rich default markdown.* styles to "none" in NEUTRAL_MARKDOWN_THEME to prevent background color leakage (e.g., black backgrounds on inline code and code blocks)
• Add regression tests ensuring no markdown.* style carries a background color
• The core fix targets markdown.code ("bold cyan on black") and markdown.code_block ("cyan on black"); additional keys (markdown.emph, markdown.h7, markdown.list) are overridden as a defensive measure

Test plan

• New unit tests verify markdown.code and markdown.code_block have no bgcolor
• Generic guard test ensures all markdown.* styles have no bgcolor
• Full test suite passes (2024 passed, 0 failed)
• Manual verification: render Markdown with inline code and fenced code blocks on light/dark terminals

Closes #1681

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[Copilot]

Pull request overview

This PR updates the shell’s Rich theme configuration to avoid Rich’s default Markdown styles introducing unintended background colors (notably for inline code and code blocks), and adds regression tests plus release-note entries documenting the fix.

Changes:

• Extend NEUTRAL_MARKDOWN_THEME to explicitly neutralize additional markdown.* styles (including markdown.code / markdown.code_block) to prevent inherited “on black” backgrounds.
• Add unit tests asserting markdown.code / markdown.code_block have no background color and attempting to guard against future markdown.* background leakage.
• Add Unreleased changelog entries (EN/ZH + root) documenting the rendering fix.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/kimi_cli/ui/shell/console.py	Adds more markdown.* theme overrides to prevent Rich default Markdown backgrounds from leaking into shell rendering.
tests/ui/test_console_theme.py	Adds regression tests asserting the theme’s Markdown-related styles don’t set a background color.
CHANGELOG.md	Adds an Unreleased entry describing the Markdown black-background fix.
docs/en/release-notes/changelog.md	Mirrors the Unreleased changelog note in English docs.
docs/zh/release-notes/changelog.md	Mirrors the Unreleased changelog note in Chinese docs.

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[Copilot]

test_all_markdown_styles_have_no_background() only iterates over NEUTRAL_MARKDOWN_THEME.styles, which contains only explicitly-defined overrides. This won’t catch cases where a markdown.* key is missing and a background color is inherited from Rich’s defaults (the main failure mode described in the docstring). Consider enumerating the markdown style names you rely on (e.g., from kimi_cli.utils.rich.markdown._FALLBACK_STYLES and any other markdown.* names used via markup) and asserting Console(theme=NEUTRAL_MARKDOWN_THEME).get_style(name).bgcolor is None for each, so missing overrides fail the test.

[Copilot]

The newly added overrides markdown.list, markdown.h7, and markdown.emph don’t appear to be referenced anywhere else in the codebase (search only finds them in this theme). If they’re intended purely as a defensive override against Rich internals, it would help to add a brief comment explaining why these keys are needed here; otherwise consider dropping unused keys to keep the theme definition aligned with actual style names we render.