feat(dashboard): add batch deletion for skills

[Ars1027]

Closes #8857

Problem

The Skills page currently supports deleting only one Skill at a time. Removing many local Skills requires users to repeat the same select, confirm, and delete flow for every item.

Skills provided by plugins or sandbox presets are read-only and must not be exposed to deletion.

Solution

This PR adds an opt-in batch selection mode to the installed Skills list.

It reuses the existing single-Skill deletion API and processes selected Skills sequentially. The list is refreshed once after all deletion attempts finish. This keeps the change frontend-only, avoids introducing a new API, and prevents a burst of concurrent deletion requests.

Failed deletions do not stop the remaining operations. Any retryable failed items remain selected after the batch completes.

Changes

• Added a selection mode to the installed Skills list.
• Added select-all, clear-selection, cancel, and delete-selected actions.
• Restricted selection to deletable local Skills.
• Excluded plugin-provided and sandbox-preset Skills from batch selection.
• Added a confirmation dialog showing the exact Skills to be deleted.
• Added sequential deletion with per-item failure handling.
• Refreshes the Skills list once after the batch completes.
• Keeps failed items selected after partial failure.
• Preserved the existing single-Skill deletion flow.
• Added English, Simplified Chinese, and Russian UI strings.
• Added focused tests for batch deletion behavior and backward compatibility.
• Refined the confirmation list styling and success feedback.

Testing

Automated verification:

cd dashboard
node --test tests/*.test.mjs
corepack pnpm@10.28.2 run typecheck
corepack pnpm@10.28.2 run build
corepack pnpm@10.28.2 exec prettier --check src/components/extension/SkillsSection.vue tests/skillsBatchDelete.test.mjs

Results:

• 44/44 Node tests passed.
• Vue TypeScript checking passed.
• Production Dashboard build passed.
• Prettier formatting check passed.

Covered scenarios:

• All selected Skills are deleted successfully.
• Requests are executed sequentially.
• A failed deletion does not prevent later deletions.
• Failed and still-deletable Skills remain selected for retry.
• Plugin-provided and sandbox-preset Skills cannot enter the deletion set.
• Empty or stale selections cannot open a destructive confirmation.
• Existing single-Skill deletion remains compatible.
• A failed post-delete refresh preserves the load error without misleading success feedback.

Manual verification was also completed against an Ubuntu Docker deployment:

• Entered and exited selection mode.
• Selected deletable local Skills.
• Confirmed the target list before deletion.
• Deleted selected Skills successfully.
• Verified read-only Skills were not selectable.
• Verified the existing single-delete flow still worked.

Screenshots

Batch selection

Deletion confirmation

Notes for Reviewer

• Sequential deletion is intentional. It reuses the existing endpoint while avoiding concurrent filesystem mutations and sandbox synchronization calls.
• The deletion targets are captured as a stable snapshot when the confirmation dialog opens.
• The existing isReadOnlySourceSkill rule is reused so batch deletion follows the same source restrictions as single deletion.
• This PR is intentionally limited to the Skills page. Plugin management is unchanged.
• No backend API, public interface, generated API client, or dependency was added.
• This is not a breaking change.

Checklist

• This is NOT a breaking change.
• The feature was discussed in [Feature]webui Need a multiple choice option #8857 and welcomed by a maintainer.
• Verification steps and test results are provided above.
• No new dependencies are introduced.
• This change does not introduce malicious code.

Summary by Sourcery

Enable safe batch deletion of locally installed Skills from the Dashboard while preserving read-only protections and existing deletion behavior.

New Features:

• Add opt-in batch selection and deletion for locally deletable installed Skills.
• Provide select-all, clear, cancel, confirmation, and partial-failure retry interactions for batch deletion.

Enhancements:

• Keep plugin-provided and sandbox-preset Skills read-only and excluded from batch deletion.
• Preserve the existing single-Skill deletion flow while refreshing the list after batch operations.

Tests:

• Add focused coverage for sequential batch deletion, failure handling, selection restrictions, refresh behavior, and single-deletion compatibility.

Chores:

• Add localized batch-deletion interface strings and supporting selection icon styling.

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

Sourcery assessment

Needs a human reviewer. A confirmed batch operation calls the delete API for every selected skill, so a selection or implementation error can permanently remove multiple stored skills. Reverting the change stops future batch deletions but cannot restore skills already deleted; the impact is bounded to the selected records.

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 5a38a2665e

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[Ars1027]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

Reviewed commit: 7e8288e1e4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".