Resolve superseded calendar approvals

[O1af]

Summary

• Deny pending Google Calendar approval requests when the user sends a new message instead of approving or denying.
• Reuse that lifecycle path for prompt submissions and suggestion clicks so stale approval cards disappear before the next turn.
• Add regression coverage for follow-up messages while an approval request is pending.

Root Cause

Prompt submissions and suggestion clicks called sendMessage directly, while only the approval buttons called addToolApprovalResponse. That left approval-requested tool parts in chat state when the user moved on with a new question.

Validation

• pnpm run test
• pnpm run lint
• pnpm run build
• pnpm run format:check attempted, but blocked by the existing formatter config trying to load vite.config.ts as an unsupported config file.

Linear: GCA-5