feat(marketing): HoM feature-spotlight X drafts + brand-voice charter (v0.18.0 B)

The Head of Marketing now markets features, not just releases: a default-off
x_feature_spotlight loop periodically spawns the HoM to investigate what shipped
(CHANGELOG, feature flags, docs/map, KB) and draft ONE held marketing post via
propose_feature_spotlight, reviewed in the X post queue.

- New x_feature source (distinct from x_post, fixing panel mislabeling) + a
  panel Feature-spotlight branch.
- brand_voice column on company_goals (migration 061, single head) as the
  CEO-editable voice source, surfaced in Settings and injected into the HoM
  briefing; a VOICE GUIDE baseline in head-marketing.md.
- propose_feature_spotlight verb (HoM-only), mirroring propose_roadmap.

Gated by x_feature_spotlight_enabled (default off; flag-off dormancy proven).
Also fixed two real bugs found mid-build: company_goals API schemas dropped
brand_voice on GET/PUT; the live charter UI is goals-tab.tsx, not the unmounted
company-goals-card.tsx. Full suite green (2935); migration single-head verified.

tests/integration/test_company_goals_routes.py

@@ -39,6 +39,19 @@ async def test_ceo_can_update_and_persist(db_session: Any) -> None:
     assert again.north_star == "Win the market"
 
 
+@pytest.mark.asyncio
+async def test_ceo_can_update_and_persist_brand_voice(db_session: Any) -> None:
+    ceo = _agent(AgentRole.CEO)
+    resp = await update_company_goals(
+        CompanyGoalsUpdate(brand_voice="Confident, dry wit."), db_session, ceo
+    )
+    assert resp.brand_voice == "Confident, dry wit."
+    # Persisted and readable by a non-CEO agent (round-trips through the
+    # Pydantic response schema, not just the service-layer dict).
+    again = await get_company_goals(db_session, _agent(AgentRole.QA))
+    assert again.brand_voice == "Confident, dry wit."
+
+
 @pytest.mark.asyncio
 async def test_non_ceo_cannot_update() -> None:
     # The CEO check fires before any DB access, so a dummy session suffices.