feat(inception): services/inception.decide() + current_defaults(); the standard Systems vocabulary moves to the service and seeds at inception (#2881, milestone 297 step 3)

- inception.decide(user, project, choices=, via=): owner-only; validates the
  choices (pure) and every target (owned rulebook / always-on for an
  exclusion / readable design system) BEFORE any effect; then, each
  idempotent: exclude always-on rulebooks, subscribe rulebooks, point the
  design system (None = explicitly none), seed the standard Systems if asked
  and the project has none; writes projects.inception LAST. Re-deciding is
  additive for exclusions/subscriptions, replaces the design system, never
  re-seeds.
- inception.current_defaults(): what binds if nobody decides — the ask's
  payload (always-on / other rulebooks, standing exclusions + subscriptions,
  design system + the choices, Systems count).
- services/systems.STANDARD_SYSTEMS (name + generic charter) + seed_standard_systems();
  mcp/tools/systems names the same list in the bootstrap ask — one vocabulary.
- Integration tests: effects land and the record says why; bad targets apply
  nothing; outsiders cannot decide.

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

tests/test_inception.py

@@ -55,3 +55,11 @@ def test_normalize_choices_is_canonical_and_complete():
                    "design_system_id": None, "seed_systems": False}
     assert normalize_choices(None) == {"exclude_always_on_rulebooks": [], "subscribe_rulebooks": [],
                                        "design_system_id": None, "seed_systems": False}
+
+
+def test_standard_systems_vocabulary_is_one_list_for_ask_and_seed():
+    from scribe.mcp.tools.systems import _STANDARD_SYSTEMS
+    from scribe.services.systems import STANDARD_SYSTEMS
+    assert _STANDARD_SYSTEMS == tuple(n for n, _ in STANDARD_SYSTEMS)
+    assert len(STANDARD_SYSTEMS) == 8 and all(charter for _, charter in STANDARD_SYSTEMS)
+