fix: replay marker-only slash skill prompts

[kocaemre]

Summary

• reconstructs marker-only model-bound slash skill prompts during history replay
• keeps client/local command metadata hidden when local stdout/stderr is present
• adds regression coverage for both string and content-array transcript shapes

Closes #998.

Verification

• npm run test:run -- src/tests/acp-agent.test.ts -t 'stripLocalCommandMetadata'
• npm run test:run -- src/tests/acp-agent.test.ts
• npm run build
• npm run check
• git diff --check

I also ran npm run test:run. It completed with 965 passing tests, 27 skipped, and the same two root-environment resolve-permission-mode failures seen when running as root: bypassPermissions is intentionally downgraded to default in that environment. The changed replay/metadata tests passed.