Extract Knowledge Base into a plugin (reference non-asset plugin)

First feature extracted from core into a plugin per "plugin is the product",
mirroring the notifications plugin. KB is a NON-asset plugin: it contributes a
model + blueprint + nav item but registers no AssetType.

- plugins/knowledgebase/: manifest.json (api_prefix /api/knowledgebase, no deps),
  models/ (KnowledgeBase, contract-pure imports via shopdb.api), api/ (the
  blueprint, same routes/prefix so the frontend is unchanged), plugin.py
  (get_blueprint + get_models + get_navigation_items).
- De-cored: removed shopdb/core/models/knowledgebase.py + api/knowledgebase.py,
  their __init__ exports, and 'knowledgebase' from CORE_BLUEPRINT_NAMES; dropped
  the hardcoded KB nav item from dashboard.py (now via the plugin nav hook).
- search.py and reports.py lazy-import KnowledgeBase from the plugin and degrade
  gracefully (search skips via _require_enabled when disabled; kb-popularity
  report returns 503 if the plugin is absent).
- Registered in instance/plugins.json (enabled).

The knowledgebase table stays in the core Alembic chain (bundled-plugin schema
folded into core, ADR-004); the model just maps it. KB was never in the
shopdb.api contract surface, so no __contract_version__ bump.

Pinned with characterization tests first (test_knowledgebase.py); they pass
unchanged against the plugin blueprint. 163 tests pass, naming green, app boots
7 bundled plugins, KB endpoint/nav/search verified live.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shopdb/core/models/__init__.py

@@ -12,7 +12,6 @@ from .relationship import AssetRelationship, RelationshipType
 from .communication import Communication, CommunicationType
 from .user import User, Role, Permission
 from .application import Application, AppVersion, AppOwner, SupportTeam
-from .knowledgebase import KnowledgeBase
 from .setting import Setting
 from .auditlog import AuditLog
 
@@ -50,7 +49,6 @@ __all__ = [
     'AppOwner',
     'SupportTeam',
     # Knowledge Base
-    'KnowledgeBase',
     # Settings
     'Setting',
     # Audit

shopdb/core/models/knowledgebase.py

@@ -1,27 +0,0 @@
-"""Knowledge Base models."""
-
-from shopdb.extensions import db
-from .base import BaseModel
-
-
-class KnowledgeBase(BaseModel):
-    """Knowledge Base article linking to external resources."""
-    __tablename__ = 'knowledgebase'
-
-    linkid = db.Column(db.Integer, primary_key=True)
-    appid = db.Column(db.Integer, db.ForeignKey('applications.appid'))
-    shortdescription = db.Column(db.String(500), nullable=False)
-    linkurl = db.Column(db.String(2000))
-    keywords = db.Column(db.String(500))
-    clicks = db.Column(db.Integer, default=0)
-    lastupdated = db.Column(db.DateTime, default=db.func.now(), onupdate=db.func.now())
-
-    # Relationships
-    application = db.relationship('Application', backref=db.backref('knowledgebase_articles', lazy='dynamic'))
-
-    def __repr__(self):
-        return f"<KnowledgeBase {self.linkid}: {self.shortdescription[:50] if self.shortdescription else 'No desc'}>"
-
-    def increment_clicks(self):
-        """Increment click counter."""
-        self.clicks = (self.clicks or 0) + 1