feat(inception): the doors — create_project/decide_project_inception take the decision, enter_project asks until decided, REST inception endpoints, _INSTRUCTIONS (#2882, milestone 297 step 4)

- MCP create_project(..., exclude_always_on_rulebooks, subscribe_rulebooks,
  design_system_id (0 unstated / -1 none / n), seed_systems): any inception
  arg → inception.decide(via="mcp") after the create; none → undecided with
  an inception_hint. New decide_project_inception(project_id, …) records or
  re-records; nothing given = an inherit-all decision, stated.
- enter_project carries `inception` ONLY for the caller's own, undecided
  project: inception_ask() = the project's current defaults + what to ask the
  operator once + the exact call (the #2683 ask shape). Absent otherwise.
- REST: POST /api/projects accepts `inception` (validated before the create);
  POST /api/projects/<id>/inception decides/re-decides; GET …/inception/defaults
  is the card's payload; GET project already carries inception via to_dict.
- _INSTRUCTIONS: ORIENT names the ask; START a project names the questions —
  never create a project bare by default (product behaviour, P#119).

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

src/scribe/services/inception.py

@@ -237,3 +237,36 @@ async def decide(
         },
     }
 
+
+async def inception_ask(user_id: int, project_id: int) -> dict:
+    """The enter_project ask for an undecided project (milestone 297) — the
+    sibling of the systems-bootstrap ask (#2683): the project's OWN current
+    defaults, what to ask the operator, and the exact call that answers it.
+    Fail-open: a hint must never break the call it rides on."""
+    try:
+        defaults = await current_defaults(user_id, project_id)
+    except Exception:
+        return {}
+    always = ", ".join(f"{r['title']} (#{r['id']})" for r in defaults["always_on_rulebooks"]) or "none"
+    others = ", ".join(f"{r['title']} (#{r['id']})" for r in defaults["other_rulebooks"]) or "none"
+    designs = ", ".join(f"{d['title']} (#{d['id']})" for d in defaults["design_systems"]) or "none"
+    return {
+        "defaults": defaults,
+        "ask": (
+            "This project has no inception decision: nobody has said what it "
+            f"inherits. Today, by default: always-on rulebooks binding it — {always}; "
+            f"rulebooks it could subscribe to — {others}; design system — "
+            f"{'#' + str(defaults['design_system_id']) if defaults['design_system_id'] else 'none'} "
+            f"(available: {designs}); Systems — {defaults['systems']}. Ask the operator, "
+            "once: which always-on rulebooks to EXCLUDE here (default: none), which "
+            "rulebooks to subscribe, which design system (or none), and whether to seed "
+            "the standard starter Systems — then record the answers. This ask repeats on "
+            "every enter_project until a decision is recorded."
+        ),
+        "call": (
+            f"decide_project_inception(project_id={project_id}, "
+            "exclude_always_on_rulebooks=[...], subscribe_rulebooks=[...], "
+            "design_system_id=<id | -1 for none>, seed_systems=<true|false>)"
+        ),
+    }
+