feat(alembic): B2 drop unused pm_approvals Task column

Smoke run analysis initially flagged three Task fields as unused
(pm_approvals, quick_context, proactive_context). A follow-up audit
found quick_context (stores original_developer marker + doc notes +
PR creator + escalation notes) and proactive_context (RAG injection)
are actively used. Only pm_approvals is truly orphaned.

Migration 014 drops pm_approvals; downgrade() recreates it if ever
needed. The two false-positive fields stay untouched.

Spec ref: docs/superpowers/specs/2026-05-12-post-smoke-3-fixes-design.md
section B2 (re-scoped 2026-05-12).

tests/integration/test_migration_014_drop_pm_approvals.py

@@ -0,0 +1,41 @@
+"""Wave B2 (2026-05-12, re-scoped): migration 014 drops pm_approvals.
+
+Original spec proposed dropping three Task columns; investigation found
+quick_context and proactive_context are actively used (original_developer
+tracking, RAG context). Only pm_approvals is truly orphaned.
+"""
+
+from __future__ import annotations
+
+import pytest
+from sqlalchemy import text
+
+
+@pytest.mark.asyncio
+async def test_pm_approvals_dropped(db_session) -> None:  # type: ignore[no-untyped-def]
+    """pm_approvals column is gone from the tasks table."""
+    result = await db_session.execute(
+        text(
+            "SELECT column_name FROM information_schema.columns "
+            "WHERE table_name = 'tasks' AND column_name = 'pm_approvals'"
+        )
+    )
+    rows = list(result)
+    assert rows == [], "pm_approvals column should have been dropped"
+
+
+@pytest.mark.asyncio
+async def test_quick_context_and_proactive_context_remain(db_session) -> None:  # type: ignore[no-untyped-def]
+    """quick_context and proactive_context MUST remain — they're actively used."""
+    result = await db_session.execute(
+        text(
+            "SELECT column_name FROM information_schema.columns "
+            "WHERE table_name = 'tasks' "
+            "AND column_name IN ('quick_context', 'proactive_context')"
+        )
+    )
+    rows = {r[0] for r in result}
+    assert "quick_context" in rows, (
+        "quick_context must remain (original_developer + audit)"
+    )
+    assert "proactive_context" in rows, "proactive_context must remain (RAG injection)"