feat(mentor): add prompt caching toggle to agent settings

[conradmugabe]

Add an "Enable prompt caching" switch to the Capabilities sub-tab of the edit-mentor settings panel, wired to the enable_prompt_caching mentor setting. Defaults to off and persists via the mentor settings endpoint, mirroring the existing enable_multi_query_rag toggle.

Checklist

• Tests were added/updated according to the feature/bugfix/change made
• Version was rolled according to semver requirements
• API endpoints openapi schema was updated if applicable

Changes

• Closes https://github.com/iblai/iblai-platform/issues/1608

Screenshots

Screencast.from.2026-06-08.06-49-08.mp4

[mamigot]

Claude finished @conradmugabe's task —— View job

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E2E Coverage Bot Review ✅

Reviewing PR #226 for E2E test coverage requirements.

Todo List:

• Step 1: Dismiss stale REQUEST_CHANGES reviews from myself
• Step 2: Identify what changed (check for new app routes)
• Step 3: Run mechanical coverage check
• Step 4: Read current coverage state
• Step 5: Apply decision logic and post review

Analysis:

• No stale reviews found to dismiss
• Files changed:
  • CHANGELOG.md (version bump)
  • components/modals/edit-mentor-modal/tabs/settings-tab.tsx (main implementation)
  • 2 test files for the settings tab
• No new app/**/page.tsx routes - this is a settings modal change, not a new route

Coverage Check Results:

• ✅ Coverage unchanged: 403 checkpoints
• ✅ Journey coverage: 24/24 files mapped (100%)
• ✅ All user-facing changes have E2E journey coverage!

Decision: CASE E - No Issues
Since no new app routes were introduced and the mechanical coverage check passed, I've approved this PR. The prompt caching toggle is a settings modal feature that doesn't require additional E2E coverage.

Review Posted: ✅ Approved with no coverage issues found.

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✅ E2E Coverage — No Issues

No new app routes were introduced. All existing coverage is intact.