Harden 2048 demo recorder validation

[willamhou]

Summary

• make the 2048 recorder fail when deepseek exec fails or required game files are missing
• print explicit transcript status and tune the prompt toward smaller retryable writes

Verification

• bash -n docs/demo/record-2048-demo.sh
• docs/demo/record-2048-demo.sh --dry-run
• docs/demo/record-2048-demo.sh --redaction-self-test
• DEEPSEEK_API_KEY=dummy DEEPSEEK_2048_BIN=/bin/true docs/demo/record-2048-demo.sh --cleanup (expected failure)
• git diff --check
• node scripts/check-secrets.js

[github-actions]

DeepSeekCode review of PR #32 (Harden 2048 demo recorder validation)

Let me examine the PR diff and the relevant files.