Add Artillery Lab with ravine send-off

[RL-Charles]

What changed

• adds a development-only Artillery Lab powered by Phaser with deterministic mock matches and live managed-agent matches
• persists live match events in channel messages so matches can be reopened and resumed
• uses five-second turns and adds launch, impact, victory, and mute-aware arena audio
• shows the losing managed agent's name on the delete action and permanently deletes that agent after confirmation
• plays a post-deletion ravine cinematic using the loser's profile image, including a descending synthesized yell and a skip control

Why

This provides a fast interactive agent-versus-agent game lab and makes the destructive loser action explicit, functional, and visually clear. The cinematic runs only after deletion succeeds, so it cannot imply an agent was removed when the operation failed.

Validation

• cd desktop && pnpm build:e2e
• node --import ./test-loader.mjs --experimental-strip-types --test src/features/games/artillery/*.test.mjs — 17 passed
• pnpm exec playwright test tests/e2e/game-lab.spec.ts --project=smoke — 5 passed
• manually exercised in the Tauri desktop app against the existing development profile and relay