feat(jetbrains): track prompt slash and mention usage

[kirillk]

Summary

• Track aggregate prompt mention usage for JetBrains conversation send/message telemetry without sending mention text or file paths
• Mark server slash command dispatches in existing conversation telemetry
• Emit a client slash command usage event for built-in JetBrains slash actions

Validation

• ./gradlew :frontend:test --tests ai.kilocode.client.session.controller.CommandLifecycleTest --tests ai.kilocode.client.session.controller.PromptLifecycleTest
• ./gradlew typecheck
• bun turbo typecheck

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• packages/kilo-jetbrains/frontend/src/main/kotlin/ai/kilocode/client/session/SessionUi.kt
• packages/kilo-jetbrains/frontend/src/main/kotlin/ai/kilocode/client/session/controller/SessionController.kt
• packages/kilo-jetbrains/frontend/src/test/kotlin/ai/kilocode/client/session/controller/CommandLifecycleTest.kt
• packages/kilo-jetbrains/frontend/src/test/kotlin/ai/kilocode/client/session/controller/PromptLifecycleTest.kt

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_{Reviewed by gpt-5.4-20260305 · Input: 199.8K · Output: 9.6K · Cached: 1.1M}

_{Review guidance: REVIEW.md from base branch main}