feat(runtime): add DeepSeek Harness engine and no-resume history

[sam2tom]

Adds agent_kind="deepseek_harness" as a fifth daemon engine, driven through the harness's only supported automation surface, dsh --profile headless <task>: one prompt is one fresh dsh process that prints the final assistant text and exits.

Verified against a real dsh install (0.1.0-rc.6 local, 0.1.0-rc.7 in an isolated prefix): the headless app takes a task positional only, its runner mints a random session id per invocation, and a second run in the same DSH_HOME/workspace has no memory of the first. The engine therefore advertises no streaming, usage, resume or permission capability, and the adapter never synthesizes a session id.

Because that leaves every turn contextless, the server now injects a bounded transcript tail into the system-prompt slot for any engine whose heartbeat descriptor reports Capabilities.Resume=false — deepseek_harness and opencode today. Gating on the live descriptor rather than an engine name list means an engine that gains resume support stops receiving a duplicate transcript as soon as it advertises it.

Daemon adapter:

• state under ~/.parsar keyed by AgentStateKey (DSH_HOME), run-scoped --patch overlay deleted on cleanup, secrets only ever in env
• managed models arrive as a declared llm-pi-ai route, reusing the pi wire-protocol mapping (both embed pi-ai)
• unattended runs declare and select a permission preset pairing workspace-write with approval:never; patching the approval row alone fails dsh boot with "composed sandbox and approval defaults match no preset" and is re-pinned per session anyway

Refactors pulled in by the new engine:

• engine preflight moves from four hand-written probe blocks in connect.go to one table in agent_cli.go (identical operator output)
• the AgentStateKey path sanitizer moves to internal/paths, shared with pi
• the duplicated formatAgentKindLabel in RuntimePage and LocalDeviceRuntimesPanel becomes agentKindDisplayName in lib/

Also threads the trigger message id through PromptInput so the injected transcript excludes the task the run is already carrying, and pins DSH_VERSION in the sandbox image.

What & why

How

Verification

• make check
• Relevant E2E target (if any): …
• Manual smoke (describe briefly)

Notes for reviewers