feat(projection): show staged projection with evidence ladder

Report a projection stage, an evidence ladder and the sustained-regime
write rate from compute_projection, per ADR 0012. A provisional lifespan
appears after 3 observed hours and carries the hours observed and a
short-horizon spread; the complete-local-day condition becomes a fact
instead of a gate, and the write rate replaces the lifespan when no
baseline applies. The TUI and CLI render the stage, ladder count and
full ladder, and drop their own two-sample pre-gates.

tests/test_projection.py

@@ -398,16 +398,16 @@ class TestArithmetic:
             _insert_day(store, d, bw=1024*1024*100)
         _insert_sample(store, "2026-09-30T10:00:00+00:00", pu=5)
         result = compute_projection(store, _clock())
-        if result.headline_remaining_seconds is not None:
-            E_rated = 1.0 * TBW_TO_BYTES
-            regime_bytes = 30 * 1024 * 1024 * 100
-            # Actual wall-clock: Sep 1 00:00 -> Sep 30 12:00 = 29.5 days
-            period_start = datetime(2026, 9, 1, 0, 0, 0, tzinfo=timezone.utc)
-            period_end = _clock()
-            actual_wc = int((period_end - period_start).total_seconds())
-            rate = regime_bytes / actual_wc
-            expected = max(E_rated - regime_bytes, 0) / rate
-            assert abs(result.headline_remaining_seconds - expected) < 1.0
+        E_rated = 1.0 * TBW_TO_BYTES
+        W_t = 512000000000  # lifetime bytes written of the newest published sample
+        regime_bytes = 30 * 1024 * 1024 * 100
+        # Actual wall-clock: Sep 1 00:00 -> Sep 30 12:00 = 29.5 days
+        period_start = datetime(2026, 9, 1, 0, 0, 0, tzinfo=timezone.utc)
+        actual_wc = int((_clock() - period_start).total_seconds())
+        rate = regime_bytes / actual_wc
+        expected = max(E_rated - W_t, 0) / rate
+        assert result.headline_remaining_seconds is not None
+        assert abs(result.headline_remaining_seconds - expected) < 1.0
 
     def test_implied_baseline_formula(self, store):
         W_t = 1024 * 1024 * 1000