[simplify interface] Migrate regnans to plant's consolidated run_scm() API + bump .plant-interface-version

[dfalster]

Follow-up after two things landed: (1) this package was renamed plant.assembly → regnans, and (2) plant's develop branch consolidated the SCM API (see traitecoevo/plant#408 and the cohort-refining post). regnans still calls helpers that were removed/renamed upstream.

What changed in plant

• build_schedule(p, ctrl) → run_scm(p, ctrl = ctrl, refine_schedule = TRUE)$parameters
• run_scm_collect(x) → run_scm(x, collect = TRUE)
• scm_base_control() → control() (fast settings are now the control()/Control() default)
• run_scm_error() / R-side build_schedule/split_times removed

To do in regnans

• Migrate call sites of the removed helpers — at least R/community_plant.R and scripts/example/ESA.Rmd (grep for build_schedule, run_scm_collect, run_scm_error, scm_base_control).
• Run the test suite against the current plant develop.
• Update .plant-interface-version — the pinned plant ref (a specific develop SHA) and the applied_breaking_changes list.

Notes

• plant develop is in flux, so pin the migration to a specific commit and expect to redo it when develop stabilises.
• Downstream: overstorey articles that exercise regnans/plant still need a re-render once plant settles (its committed _freeze/ output is stale and still references the old plant.assembly name).
• Cross-package context & the migration playbook: plant-meta → governance/release-playbooks.md (§1).