feat: add dsh (DeepSeek Harness) transcript source

[rmax]

Summary

Add dsh as a first-class DeepSeek Harness transcript source.

DeepSeek Harness persists append-only session logs as .jsonl.zstd; the adapter accepts decompressed JSONL text, so zstd remains a caller/container concern and no dependency was added.

Event mapping

• session supplies session metadata
• request/header / request/context supply model metadata
• user/message and aggregate assistant/message supply text and reasoning
• direct tool/call and tool/result supply linked tool lifecycle records
• streaming chunks and structural/permission/title metadata are ignored

The source also supports local listing of compressed session paths.

Validation

• Sanitized fixture covers headers, turns, user/assistant messages, reasoning, tool call/result pairing, and ignored chunks
• Tests cover happy path, malformed-line tolerance, chunk omission, pairing, canonical identity, and listing
• bun run check
• Python wrapper tests
• Privacy-safe normalization smoke test against a real decompressed dsh session

Fixtures are aggressively anonymized; no personal paths, identifiers, credentials, emails, or transcript content were retained.