feat(entities): inbox + cross-project (project="") support (Issue C)

Makes `inbox` a reserved pseudo-project and `project=""` a first-class
cross-project bucket. Unblocks AKC capturing pre-project leads/quotes
and cross-project facts (materials, vendors) that don't fit a single
registered project.

- projects/registry.py: INBOX_PROJECT/GLOBAL_PROJECT constants,
  is_reserved_project(), register/update guards, resolve_project_name
  passthrough for "inbox"
- engineering/service.py: get_entities scoping rules (inbox-only,
  global-only, real+global default, scope_only=true strict).
  promote_entity accepts target_project to retarget on promote
- api/routes.py: GET /entities gains scope_only; POST /entities accepts
  project=null as ""; POST /entities/{id}/promote accepts
  {target_project, note}
- engineering/wiki.py: homepage shows "Inbox & Global" cards with live
  counts linking to scoped lists
- tests/test_inbox_crossproject.py: 15 tests (reserved enforcement,
  scoping rules, API shape, promote retargeting)
- DEV-LEDGER.md: session log, test_count 463 -> 478

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/atocore/projects/registry.py

@@ -11,6 +11,20 @@ import atocore.config as _config
 from atocore.ingestion.pipeline import ingest_folder
 
 
+# Reserved pseudo-projects. `inbox` holds pre-project / lead / quote
+# entities that don't yet belong to a real project. `""` (empty) is the
+# cross-project bucket for facts that apply to every project (material
+# properties, vendor capabilities). Neither may be registered, renamed,
+# or deleted via the normal registry CRUD.
+INBOX_PROJECT = "inbox"
+GLOBAL_PROJECT = ""
+_RESERVED_PROJECT_IDS = {INBOX_PROJECT}
+
+
+def is_reserved_project(name: str) -> bool:
+    return (name or "").strip().lower() in _RESERVED_PROJECT_IDS
+
+
 @dataclass(frozen=True)
 class ProjectSourceRef:
     source: str
@@ -56,8 +70,17 @@ def build_project_registration_proposal(
     normalized_id = project_id.strip()
     if not normalized_id:
         raise ValueError("Project id must be non-empty")
+    if is_reserved_project(normalized_id):
+        raise ValueError(
+            f"Project id {normalized_id!r} is reserved and cannot be registered"
+        )
 
     normalized_aliases = _normalize_aliases(aliases or [])
+    for alias in normalized_aliases:
+        if is_reserved_project(alias):
+            raise ValueError(
+                f"Alias {alias!r} is reserved and cannot be used"
+            )
     normalized_roots = _normalize_ingest_roots(ingest_roots or [])
     if not normalized_roots:
         raise ValueError("At least one ingest root is required")
@@ -129,6 +152,10 @@ def update_project(
     ingest_roots: list[dict] | tuple[dict, ...] | None = None,
 ) -> dict:
     """Update an existing project registration in the registry file."""
+    if is_reserved_project(project_name):
+        raise ValueError(
+            f"Project {project_name!r} is reserved and cannot be modified"
+        )
     existing = get_registered_project(project_name)
     if existing is None:
         raise ValueError(f"Unknown project: {project_name}")
@@ -272,6 +299,8 @@ def resolve_project_name(name: str | None) -> str:
     """
     if not name:
         return name or ""
+    if is_reserved_project(name):
+        return name.strip().lower()
     project = get_registered_project(name)
     if project is not None:
         return project.project_id