fix(skills): group installed skills by agent and keep mention names static

[kev1n77]

Summary

• Group installed skills dynamically by source, such as Claude Code and Codex, while retaining user/project scope labels.
• Remove name, scope, and shadowing tooltips from the installed list; keep click-to-open details.
• Keep @skill names static on one line and expand the picker to fit them, with marquee animation only for descriptions.
• Update English, Simplified Chinese, and Traditional Chinese strings.

Type and Areas

Type: Bug fix / UI/UX

Areas: Web UI — Skills management, chat context picker, and internationalization.

Motivation / Impact

Skills discovered from other agents previously appeared under the user or project groups, making them difficult to manage by source. Dedicated source groups now provide separate counts that remain stable during searches.

Skill names in the @skill picker previously used marquee animation. Names now remain static for easier identification and selection.

Verification

The following checks passed:

• pnpm run check:web
• pnpm run i18n:audit — 0 warnings.
• git diff --check
• Focused tests below — 4 files and 28 tests passed.

pnpm --dir src/web-ui exec vitest run src/app/scenes/skills/hooks/useInstalledSkills.test.tsx src/infrastructure/config/skillSourcePresentation.test.ts src/app/scenes/skills/SkillsScene.presentation.test.ts src/flow_chat/components/ChatContextPickerOverlay.test.tsx

pnpm run motion:audit was also executed. It produces an animation inventory rather than a pass/fail gate.

Verification ran locally. No live end-to-end verification was performed for remote workspaces, remote control, Peer Device Mode, or Detached Dispatch.

Reviewer Notes

• Source grouping uses stable source identifiers and supports legacy source aliases.
• Changes are limited to frontend presentation; skill discovery, runtime precedence, and persisted formats are unchanged.
• Picker width remains constrained by the viewport. Automated tests do not establish visual correctness on a running desktop.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.