fix(cli): require explicit non-interactive init source

[miguel-heygen]

Summary

• fail non-interactive init when no --example, --video, or --audio source is provided
• prevent silent scaffolding of an empty 10-second black composition that passes check
• update CLI examples to pass --example blank explicitly
• add regression coverage that asserts failure leaves no project directory

Reproduction

HYPERFRAMES_SKIP_SKILLS=1 npx --yes hyperframes@0.7.56 init demo --non-interactive exits 0, creates a blank 10-second composition, and check --json reports zero findings.

Verification

• regression test failed before fix and passes after fix
• bunx vitest run packages/cli/src/commands/init.test.ts (22/22)
• bun run --filter @hyperframes/cli typecheck
• targeted oxfmt and oxlint clean
• branch CLI exits 1 with the actionable source requirement and creates no project
• pre-commit gates passed

Human review required; do not self-merge.