feat(portfolio): complete RESOURCE-WP-0003 T06 optimization cases and T07 reporting

T06: optimization-case schema, fail-closed evaluator, cadence and decision
template. Every option including the baseline must present all ten decision
fields; one unknown blocks the comparison. Validated on the storage case
(Hetzner computes and loses to Scaleway by EUR 29.14/month on operator labour;
Host Europe blocks on four named gaps) and on the non-storage reef-railiance
k3s rightsizing case (low utilization is real, but nothing is costable while
the railiance01 price is unknown).

T07: portfolio report over coverage, lifecycle, utilization, cost, renewals,
risks, open cases, and next actions, derived only from committed evidence.
Portfolio spend is reported null rather than as a partial sum, unattributed
cost is a named list rather than a spread, and unmeasurable resources are
reported rather than dropped.

RESOURCE-WP-0003 is finished; both cases remain blocked_on_evidence against
live delegated records in other repositories. RESOURCE-WP-0002 is untouched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_variance.py

@@ -0,0 +1,25 @@
+import sys
+import unittest
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parents[1] / "tools"))
+from variance import compare
+
+
+class VarianceTest(unittest.TestCase):
+    def test_reports_signed_error_and_absolute_percentage_error(self):
+        base = {"period":"2026-09","database_gb":5,"stored_gb":100,"wal_gb":10,"restore_egress_gb":5,"write_requests":100,"read_requests":50,"infrastructure_eur":10,"internal_labor_hours":1,"internal_labor_eur":60,"total_eur":70}
+        actual_row = dict(base, stored_gb=120, infrastructure_eur=12, total_eur=72)
+        result = compare({"created_at":"2026-08-10T00:00:00Z","rows":[base]}, {"provider_id":"test","rows":[actual_row]})
+        stored = result["rows"][0]["metrics"]["stored_gb"]
+        self.assertEqual(20, stored["error"])
+        self.assertEqual(20, stored["absolute_percentage_error"])
+
+    def test_zero_forecast_has_no_percentage_error(self):
+        base = {"period":"2026-09","database_gb":0,"stored_gb":0,"wal_gb":0,"restore_egress_gb":0,"write_requests":0,"read_requests":0,"infrastructure_eur":0,"internal_labor_hours":0,"internal_labor_eur":0,"total_eur":0}
+        result = compare({"created_at":"x","rows":[base]}, {"provider_id":"test","rows":[dict(base, wal_gb=1)]})
+        self.assertIsNone(result["rows"][0]["metrics"]["wal_gb"]["absolute_percentage_error"])
+
+
+if __name__ == "__main__":
+    unittest.main()