feat(vscode): control queued follow-up messages

[patroza]

Summary

• project the authoritative server follow-up queue into the VS Code chat view
• show queued follow-ups above the composer with the same Steer and Remove actions as web/mobile
• label mid-turn submissions as Queue while retaining the server queue-by-default behavior
• dispatch thread.queue.steer and thread.queue.remove through the synchronized T3 client

Cross-client parity

• Web / desktop: existing queued chips with Steer and Remove
• Mobile: existing server queue controls plus its offline-only durable outbox
• Discord: queue-by-default lifecycle merged in feat(discord-bot): mid-turn queue default + steer/queue lifecycle #67
• VS Code: completed by this PR

Verification

• pnpm --filter t3-code test (28 passed)
• pnpm --filter t3-code typecheck
• pnpm --filter t3-code build
• targeted Vite+ formatting/lint on the three changed files