feat: add scenario analysis workspace

apps/api/migrations/202606240006_scenario_runs.sql

@@ -0,0 +1,18 @@
+CREATE TABLE IF NOT EXISTS app.scenario_runs (
+    scenario_run_id BIGSERIAL PRIMARY KEY,
+    name TEXT NOT NULL,
+    target_month TEXT NOT NULL CHECK (target_month ~ '^[0-9]{4}-[0-9]{2}$'),
+    area_id TEXT REFERENCES silver.areas(area_id),
+    interest_rate_delta_bps DOUBLE PRECISION NOT NULL DEFAULT 0,
+    policy_signal_delta INTEGER NOT NULL DEFAULT 0 CHECK (policy_signal_delta BETWEEN -4 AND 4),
+    supply_delta_pct DOUBLE PRECISION NOT NULL DEFAULT 0 CHECK (supply_delta_pct BETWEEN -100 AND 500),
+    rent_delta_pct DOUBLE PRECISION NOT NULL DEFAULT 0 CHECK (rent_delta_pct BETWEEN -80 AND 200),
+    notes TEXT NOT NULL DEFAULT '',
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_scenario_runs_month
+    ON app.scenario_runs(target_month, scenario_run_id DESC);
+
+CREATE INDEX IF NOT EXISTS idx_scenario_runs_area
+    ON app.scenario_runs(area_id, scenario_run_id DESC);