fix(systems): sweeps are the discovery moment — zero-Systems hint, create_system dedup gate, prose inverted

First real-world test of the #2562 fixes (Scribe issue #2569): a Forge
session ran a whole-codebase audit and created zero Systems — endorsed
by the shipped guidance, whose "no particular area takes none" clause
read as an exemption for exactly the record type that enumerates the
subsystem vocabulary. And the systems_hint was silent for a zero-Systems
project, the one state nothing else nudges out of.

- systems_hint gains a zero-Systems branch: prompt the FIRST
  create_system instead of going quiet.
- create_system is duplicate-gated like the other creates (normalized
  name, archived included, fail-open) — liberal creation becomes safe by
  construction, so the guidance can stop preaching restraint.
- Prose inverted on every surface (hint text, create_system docstring,
  floor bullet, using-scribe step 7): audits/sweeps take several tags
  and mint the Systems they name; the gate is the guardrail against
  sprawl, not holding back; only a record genuinely about no particular
  area goes untagged.
- Plugin 0.1.26 -> 0.1.27.

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

src/scribe/mcp/tools/systems.py

@@ -30,13 +30,24 @@ async def untagged_systems_hint(user_id: int, project_id: int) -> str | None:
     except Exception:
         return None
     if not systems:
-        return None
+        # Zero Systems is the one state nothing else nudges out of: the hint
+        # below needs a vocabulary to name, so without this branch the FIRST
+        # create_system depends entirely on prose that demonstrably doesn't
+        # fire at write time (#2562).
+        return (
+            "Created untagged — this project has no Systems yet. If this "
+            "record is about a code subsystem/area, create_system it (name + "
+            "a one-paragraph charter) and tag the record. An audit or sweep "
+            "that names areas is exactly the moment to mint them; the "
+            "duplicate gate is what guards against sprawl, not holding back."
+        )
     names = ", ".join(f"#{s.id} {s.name}" for s in systems)
     return (
         f"Created untagged. This project's Systems: {names}. If this record is "
-        "about one of those areas, tag it (update it with system_ids=[...]); if "
-        "its area is missing, create_system it and tag; if it is about no "
-        "particular area, leave it untagged."
+        "about one or more of those areas, tag it (update it with "
+        "system_ids=[...]) — cross-cutting records like audits take several; "
+        "if an area it names is missing, create_system it and tag; only leave "
+        "it untagged if it is about no particular area."
     )
 
 
@@ -54,17 +65,46 @@ async def create_system(
     Create one the moment two records would share an area that has no System
     yet — the same two-or-more test snippets use. Don't wait to be asked to
     name an area that plainly exists in the code; an unmodelled area means
-    every record about it stays untaggable. Give it a one-paragraph charter,
-    not just a label: the description is what tells a later session whether a
-    record belongs here.
+    every record about it stays untaggable. An audit or sweep that walks the
+    codebase is a DISCOVERY moment: mint the Systems it names as it names
+    them — the duplicate gate below, plus reviewing the existing list, is what
+    guards against sprawl, not holding back. Give each one a one-paragraph
+    charter, not just a label: the description is what tells a later session
+    whether a record belongs here.
 
     Args:
         project_id: The project this system belongs to (required).
         name: Short label (required).
         description: What the system is and how it's used — a name is rarely enough.
         color: Optional UI accent (hex), or empty.
+
+    Duplicate-gated like the other creates: if a System with the same
+    normalized name already exists in this project (archived included), the
+    call returns {"duplicate": true, "existing_id": ...} instead of creating —
+    tag records to that one, or update_system it if its charter needs work.
     """
     uid = current_user_id()
+    norm = " ".join(name.split()).lower()
+    if norm:
+        try:
+            existing = await systems_svc.list_systems(
+                uid, project_id, include_archived=True
+            )
+        except Exception:
+            existing = []
+        for s in existing:
+            if " ".join(s.name.split()).lower() == norm:
+                return {
+                    "duplicate": True,
+                    "existing_id": s.id,
+                    "message": (
+                        f"System '{s.name}' (#{s.id}) already covers this area "
+                        "in this project. Tag records to it with system_ids, "
+                        "or update_system it if the charter needs revising — "
+                        "a second System with the same name would split the "
+                        "area's records across two piles."
+                    ),
+                }
     system = await systems_svc.create_system(
         uid, project_id=project_id, name=name,
         description=description or None, color=color or None,