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/unit/services/test_company_goals_service.py

@@ -28,6 +28,7 @@ async def test_get_returns_empty_defaults_when_unset(db_session: Any) -> None:
     assert goals["objectives"] == []
     assert goals["constraints"] == []
     assert goals["operating_policy"] == {}
+    assert goals["brand_voice"] == ""
 
 
 @pytest.mark.asyncio
@@ -68,3 +69,23 @@ async def test_upsert_is_singleton_and_partial(db_session: Any) -> None:
     # Exactly one row exists (singleton), found at the canonical id.
     row = await db_session.get(CompanyGoalsTable, SINGLETON_ID)
     assert row is not None
+
+
+@pytest.mark.asyncio
+async def test_brand_voice_roundtrips(db_session: Any) -> None:
+    svc = get_company_goals_service(db_session)
+    await svc.upsert({"brand_voice": "Confident, dry wit, no exclamation points."})
+    goals = await svc.get()
+    assert goals["brand_voice"] == "Confident, dry wit, no exclamation points."
+
+
+@pytest.mark.asyncio
+async def test_brand_voice_untouched_by_partial_upsert(db_session: Any) -> None:
+    svc = get_company_goals_service(db_session)
+    await svc.upsert({"brand_voice": "Speak as 'we'."})
+    # A later partial upsert that omits brand_voice must leave it unchanged —
+    # the same partial-update contract north_star/constraints already have.
+    await svc.upsert({"north_star": "Ship a delightful product"})
+    goals = await svc.get()
+    assert goals["brand_voice"] == "Speak as 'we'."
+    assert goals["north_star"] == "Ship a delightful product"