research/probe: end-to-end smoke test endpoint (skip topics/loops/spawn)

New: POST /api/research/probe — one-shot pipeline probe against the
workspace's shared ZeroClaw gateway. Drives a trivial 'reply OK'
turn via ZeroClawDriveExecutor::drive and reports per-step timings.

Purpose: stop guessing what's broken in the wizard flow by exercising
JUST the executor→daemon→claude→response path. If probe succeeds
within a few seconds, we know:
- ZEROCLAW_TOKEN + gateway URL config is correct
- Daemon can reach and authenticate against claude
- The full ws round-trip works
…and every other failure we've been chasing (turn timed out, LLM
request failed, ws connect DNS error, etc.) is spawn-config or
prompt-size specific.

Request body (both optional):
  { "prompt": "Reply OK", "agent": "coordinator" }

Response:
  {
    "verdict": "ok" | "fail",
    "total_duration_ms": …,
    "prompt_len": …,
    "response_preview": "OK",
    "steps": [
      { name: "build_executor", duration_ms: …, status: "ok" },
      { name: "drive_turn",     duration_ms: …, status: "ok", detail: "tokens=N, output_len=M" }
    ]
  }

Wire-up:
- new routes/probe.rs
- pub mod probe in routes/mod.rs
- POST /api/research/probe registered in lib.rs router
- ZeroClawDriveExecutor::drive promoted from private to pub so the
  probe handler can call it (behavior unchanged, other callers were
  all inside the same struct).

Usage from anywhere (curl, browser dev tools, etc.):
  curl -X POST https://clawmates.work/api/research/probe \
    -H "Content-Type: application/json" \
    -H "Cookie: <session cookie>" \
    -d '{}'

Follow-up: a small frontend button (e.g. bottom of ResearchList) that
POSTs this and renders the response inline, so users don't need to
curl. Skipping in this commit to ship the useful part first.

crates/cm-api/src/routes/mod.rs

@@ -17,6 +17,7 @@ pub mod nodes;
 pub mod oauth;
 pub mod orgs;
 pub mod planner;
+pub mod probe;
 pub mod repos;
 pub mod research;
 pub mod research_pipeline;