feat(branding): add plugin icon from the new ShellTime logo

[AnnatarHe]

Summary

Right now the plugin has no logo, so the Marketplace and the IDE plugin manager show the default placeholder. This PR adds one, based on the new ShellTime logo from shelltime/web#657 (src/assets/logo/logo.github.svg).

• src/main/resources/META-INF/pluginIcon.svg: logo.github.svg with only the size changed, to 40×40. The 256 viewBox stays.
• src/main/resources/META-INF/pluginIcon_dark.svg: the same geometry in the web's existing dark palette from logo.ios.dark.svg: a #0f172a to #1e293b background, the arc and dot in #60a5fa, and the chevron in #93c5fd. The IDE uses it automatically on dark themes.
• The IntelliJ Platform finds both files by naming convention, so plugin.xml and build.gradle.kts don't change.
• README.md: adds the logo centered at the top, above <!-- Plugin description -->, so the Marketplace description built from the README doesn't change.

Verification

• Both SVGs pass xmllint --noout. Rendered in Chromium at 40px and 160px on light and dark backgrounds, they look right.
• I couldn't run ./gradlew buildPlugin in my environment: Maven Central returned 429, and the JetBrains host the IntelliJ Platform download needs is unreachable. CI will run the real build.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GRR68kM5sbWqBV1aHyeyug

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[claude]

Review

Small, clean PR. The icons follow the IntelliJ naming convention (pluginIcon.svg / pluginIcon_dark.svg in META-INF), so no plugin.xml or Gradle change is needed. I found no bugs or security issues. SVGs contain no scripts or external references, and there is no runtime or performance impact.

Notes (non-blocking)

• README image path: src/main/resources/META-INF/pluginIcon.svg is a relative path. It renders on GitHub, but the Marketplace description is built from the README, and the logo sits above <!-- Plugin description --> so it is excluded. That is the intended behaviour. If you ever move it inside the markers, switch to an absolute URL.
• Square background: the <rect> is a full-bleed square with no rounded corners. JetBrains guidelines allow this, and the IDE doesn't crop it. If you want a softer look in the plugin manager, add rx to the rect.
• Size: the JetBrains guidelines ask for 40×40 (the Marketplace listing uses a 256 version). The 256 viewBox scales fine, so this is OK.
• Dark variant: the dark palette is reasonable. The #0f172a background against the #60a5fa arc has good contrast.
• Tests: none are applicable. CI buildPlugin and verifyPlugin are the real check, since the build wasn't run locally. Please confirm they pass before merging.

LGTM once CI is green.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

❌ Your project check has failed because the head coverage (14.21%) is below the target coverage (60.00%). You can increase the head coverage or adjust the target coverage.

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  Coverage   14.21%   14.21%           
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  Files          20       20           
  Lines         802      802           
  Branches      184      184           
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  Hits          114      114           
  Misses        669      669           
  Partials       19       19           

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