`plan generate` records no run metadata under .maverick/runs/

Minor, found during the #135 subtask 5 walkthrough.

`maverick plan generate greet-cli --from-prd docs/greet-cli-prd.md`
completed successfully and wrote:

```
.maverick/plans/greet-cli/flight-plan.md
.maverick/plans/greet-cli/preflight-briefing.md
```

but created no `.maverick/runs//` directory. `refuel`, `fly` and
`land --status` all do.

#135 subtask 5 lists `.maverick/runs//` among the locations to
check artifacts land in, so either:

* plan generate should mint a run record like its siblings, or
* it legitimately has no run identity and the docs should say so.

Worth resolving either way so the artifact contract is unambiguous. The
cost of the current state is small but real: a plan generation that
takes ~6 minutes and 5 model calls leaves no cost/telemetry record tied
to a run id, while every other long-running op does.

(Cost *was* recorded to the runway episodic store — 5 entries with real
token counts — so this is about run identity, not telemetry loss.)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Start by comparing `plan generate` with `refuel`, `fly`, and `land --status`, then review #135 subtask 5 and the `.maverick/plans/` and `.maverick/runs//` artifact locations. Done means the run-identity behavior is resolved consistently and the artifact contract clearly states where plan-generation metadata belongs.

Written by the indexing model from the issue text.