fix(shell): correct /usage remaining quota colors

[binichallein]

Related Issue

Resolve #2019

Description

This fixes the inverted quota colors in /usage.

Root cause:

• _ratio_color() receives the remaining-quota ratio ((limit - used) / limit), not the used ratio
• the thresholds were previously mapped as if larger values were more dangerous, so high remaining quota rendered red and low remaining quota rendered green

Changes:

• map <= 10% left to red
• map <= 30% left to yellow
• map > 30% left to green
• add a regression test covering remaining-quota thresholds and over-limit behavior

This is equivalent to the common used-quota thresholds:

• < 70% used => green
• 70%-89% used => yellow
• >= 90% used => red

Checklist

• I have read the CONTRIBUTING document.
• I have linked the related issue, if any.
• I have added tests that prove my fix is effective or that my feature works.
• I have run make gen-changelog to update the changelog.
• I have run make gen-docs to update the user documentation.

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[devin-ai-integration]

Devin Review found 1 potential issue.

View 2 additional findings in Devin Review.

[devin-ai-integration]

🟡 English changelog manually edited instead of auto-synced from root CHANGELOG.md

docs/en/release-notes/changelog.md is directly edited in this PR, but docs/AGENTS.md:185 explicitly states: "The English changelog (docs/en/release-notes/changelog.md) is auto-generated from the root CHANGELOG.md. Do not edit it manually." The authoring workflow at docs/AGENTS.md:27 also says: "For changelog: edit the root CHANGELOG.md, then run npm run sync to update the English docs." The correct workflow is to only edit the root CHANGELOG.md and let the sync script (docs/scripts/sync-changelog.mjs) generate the English docs version.

Prompt for agents

The file docs/en/release-notes/changelog.md should not be manually edited. According to docs/AGENTS.md (line 185 and line 27), the correct workflow is to edit only the root CHANGELOG.md and then run 'npm run sync' from the docs/ directory to auto-generate the English changelog. Remove the manual edits from docs/en/release-notes/changelog.md and rely on the sync script to propagate the changes from CHANGELOG.md.

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[binichallein]

I initially resolved the changelog conflict manually, but I corrected the workflow afterward.

The current state follows the repo rules:

• CHANGELOG.md is the source of truth
• docs/en/release-notes/changelog.md was regenerated via node docs/scripts/sync-changelog.mjs
• docs/zh/release-notes/changelog.md was merged accordingly as the translated page

[sunmy2019]

You misunderstood the problem and gave a wrong fix.

[sunmy2019]

Usually people gave

0 < used < 70%, green
70% < used < 90%, yellow
90% < used < 100%, red

This is common practice and claude code also obeys.

green under 70%, yellow 70-89%, red 90%+

https://code.claude.com/docs/en/statusline#display-multiple-lines

[binichallein]

@sunmy2019 Thanks for catching this. You were right that my initial fix misunderstood the metric.

I've updated the PR so _ratio_color() now uses the remaining quota ratio correctly:

• <= 10% left => red
• <= 30% left => yellow
• > 30% left => green

That matches the usual used-quota thresholds after converting from remaining quota. I also added regression tests and resolved the changelog/docs conflicts following the repo workflow (CHANGELOG.md -> sync English changelog -> update Chinese changelog).

Latest update is in 4137323a. Please take another look when convenient.