Two new tables and three new columns on `scenario` to give the
ProjectionLab-style UI a place to land:
- `scenario` gains `kind` (cartesian | user), `name`, `description`,
`parent_scenario_id`. Existing Cartesian flow keeps `kind='cartesian'`
by default; user-defined scenarios point `parent_scenario_id` at the
base they cloned from (NULL for root).
- `life_event` — timed events on a scenario timeline: retirement, kid
born, mortgage payoff, sabbatical, inheritance, etc. `year_start` and
`year_end` are scenario-relative (year 0 = today).
`delta_gbp_per_year` covers ranged effects; `one_time_amount_gbp`
covers one-shot impacts. `enabled` lets the UI toggle without delete.
- `retirement_goal` — user-defined success criteria (target_nw,
never_run_out, inheritance, ...). `comparator` + `success_threshold`
let the goal say "≥ £2M at year 25 in ≥ 90% of paths".
Migration 0002 adds the columns + tables idempotently.
145 tests; mypy strict + ruff clean.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
