feat: add 0github diff themes

[lawrencecchen]

Summary

• add 0github-dark and 0github-light diff theme presets derived from the manaflow 0github palette
• add unit coverage for theme parsing and representative light/dark palette values
• document the new presets in the diff theme README section

Test Plan

• cargo test 0github
• cargo test

Notes

• cargo test currently fails on upstream/main in vcs::git::tests::test_get_merge_base_returns_ancestor
• reproduced the same failure on a clean upstream/main worktree; the failing path is src/vcs/test_utils.rs assuming refs/heads/main exists after git2 repo init

Summary by CodeRabbit

• New Features

  • Added GitHub Dark and Light themes to available diff viewer themes.

• Documentation

  • Updated configuration examples and theme reference documentation to include the new GitHub Dark and Light theme options.

[coderabbitai]

📝 Walkthrough

Walkthrough

Two new GitHub-themed color schemes (0github-dark and 0github-light) are added to the diff viewer theme system, including new enum variants, string parsing support, theme constructors, unit tests, and documentation updates reflecting the new theme options.

Changes

Cohort / File(s)	Summary
Documentation Updates README.md	Updated theme configuration examples and added "0github" entry to the available themes table.
Theme System Implementation src/command/diff/theme.rs	Added ZeroGithubDark and ZeroGithubLight enum variants to ThemePreset, updated FromStr parsing to recognize "0github-dark" and "0github-light" strings, implemented Theme::zero_github_dark() and Theme::zero_github_light() constructors with full color palettes, extended from_preset() to map new variants to constructors, and added unit tests for parsing and color validation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• fix(ui): ensure explicit background rendering for light and dark themes #111: Modifies theme color values and background handling in src/command/diff/theme.rs, directly overlaps with theme palette customization.
• Add configurable color themes for diff viewer #85: Introduces the preset/theme infrastructure foundation that this PR extends with new theme variants.

Poem

🐰 Two new themes hop into sight,
GitHub dark and GitHub light,
Color palettes, parsed with care,
Fresh shades blooming everywhere! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 27.27% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: add 0github diff themes' clearly and concisely summarizes the main change: adding two new theme presets (0github-dark and 0github-light) to the diff viewer functionality.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (1)

src/command/diff/theme.rs (1)

367-378: Consider reviewing deleted_bg and context_bg visual distinction.

Both deleted_bg (line 371) and context_bg (line 374) are set to pure white Color::Rgb(255, 255, 255), making deleted lines visually indistinguishable from context lines by background color alone. Other light themes use a subtle red/pink tint for deleted_bg.

This may be intentional to match GitHub's styling (which relies more heavily on gutter colors), but could reduce at-a-glance readability compared to other themes. Verify this matches the desired 0github palette behavior.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/command/diff/theme.rs` around lines 367 - 378, The deleted_bg and
context_bg in the DiffColors initialization are both pure white (deleted_bg and
context_bg), which makes deleted lines visually indistinguishable; update the
DiffColors struct initialization to give deleted_bg a subtle red/pink tint
(e.g., a very light pink close to the theme palette) while leaving context_bg as
white, or explicitly document/confirm the intent if pure white was deliberate;
locate the DiffColors block (the DiffColors instance where
added_bg/added_gutter_bg/.../deleted_word_bg are set) and change deleted_bg to a
slightly tinted RGB value that matches the 0github palette, then run a visual
check to ensure contrast with context_bg.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@src/command/diff/theme.rs`:
- Around line 367-378: The deleted_bg and context_bg in the DiffColors
initialization are both pure white (deleted_bg and context_bg), which makes
deleted lines visually indistinguishable; update the DiffColors struct
initialization to give deleted_bg a subtle red/pink tint (e.g., a very light
pink close to the theme palette) while leaving context_bg as white, or
explicitly document/confirm the intent if pure white was deliberate; locate the
DiffColors block (the DiffColors instance where
added_bg/added_gutter_bg/.../deleted_word_bg are set) and change deleted_bg to a
slightly tinted RGB value that matches the 0github palette, then run a visual
check to ensure contrast with context_bg.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: a83f18da-53af-48e3-be49-9811ea836134

📥 Commits

Reviewing files that changed from the base of the PR and between c0797c5 and 4b97d88.

📒 Files selected for processing (2)

• README.md
• src/command/diff/theme.rs