Phase 6: simplify-pass policy, plugins listing, roadmap to 1.0

End-of-pipeline cleanup. No structural changes; documents what is
done, what is left, and the discipline for future cleanup commits.

Skill:
- simplifying-python: end-of-session cleanup discipline. Inspired by
  Anthropic's open-sourced code-simplifier. Targets duplication, dead
  code, voodoo constants, stale comments, misnamed identifiers,
  unnecessary abstraction. Anti-targets: architecture, public API
  surface, schema, sweeping rewrites. Behavior preservation enforced
  by running pytest before and after.

Simplify pass on shopdb/utils/responses.py:
- error_response docstring claimed the error info lives at top level
  `error`. Implementation puts it under `data.error` (consistent with
  the success envelope). Implementation is correct; docstring updated.
- paginated_response docstring used snake_case keys (`per_page`,
  `total_pages`, etc). Implementation uses lowercase concatenated per
  CONTRIBUTING.md. Docstring updated to match.

Documentation:
- docs/PLUGINS.md: bundled plugins (six, with what they track and
  caveats per ADR), planned plugins (measuringtools as the scaffold
  canary per ADR-005), distribution conventions for sister-site
  plugins per ADR-003, naming policy.
- docs/ROADMAP.md: phase status table (0-5 done, 6 in progress),
  must-have work for 1.0 (Asset.mapx/mapy, equipment migration,
  printers retirement, frontend hook contract, per-plugin Alembic
  chains), nice-to-have (measuringtools plugin, frontend scaffolding,
  marketplace listing, surface-diff tooling), deferred (multi-tenancy,
  pip-installable plugins, event bus). Defines what 1.0.0 means as a
  contract.

Test count unchanged: 101 passing. Naming/style check green.

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

shopdb/utils/responses.py

@@ -80,16 +80,21 @@ def error_response(
     details: Dict = None,
     http_code: int = 400
 ):
-    """
-    Error response helper.
+    """Error response helper.
 
     Response format:
     {
         "status": "error",
-        "error": {
-            "code": "VALIDATION_ERROR",
-            "message": "Human-readable message",
-            "details": {...}
+        "data": {
+            "error": {
+                "code": "VALIDATION_ERROR",
+                "message": "Human-readable message",
+                "details": {...}
+            }
+        },
+        "meta": {
+            "timestamp": "...",
+            "requestid": "..."
         }
     }
     """
@@ -132,8 +137,7 @@ def paginated_response(
     total: int,
     schema=None
 ):
-    """
-    Paginated list response.
+    """Paginated list response.
 
     Response format:
     {
@@ -142,11 +146,11 @@ def paginated_response(
         "meta": {
             "pagination": {
                 "page": 1,
-                "per_page": 20,
+                "perpage": 20,
                 "total": 150,
-                "total_pages": 8,
-                "has_next": true,
-                "has_prev": false
+                "totalpages": 8,
+                "hasnext": true,
+                "hasprev": false
             }
         }
     }