predictalot v1.0.0 — tabular ML surface + FM extras + /v1/timeseries/ prefix

Stable API surface. Future breaking changes require a major bump.

Breaking: all FM routes move to /v1/timeseries/<type>/…. Old paths return
404. Sibling family at /v1/tabular/ ships in this release.

Tabular ML: 9 backends + 3 meta-learners (calibrated, stacking,
diversified). Lazy-loaded; dev image keeps importing the package without
the heavy ML wheels.

FM additions: ForecastConfig.extra (per-call escape hatch into backend
adapters) and ensemble memberOverrides (per-slug partial-config shadow).