Extract slideshow into a plugin (blueprint-only display plugin)

Second core feature pulled into a plugin. Slides is the minimal plugin shape:
a blueprint only - no model, no AssetType, no nav (it is purely an API surface
consumed by the TV dashboard).

- plugins/slides/: manifest (api_prefix /api/slides, no deps), api/ (moved
  blueprint, contract-pure imports via shopdb.api, same /api/slides route so the
  TV dashboard is unchanged), plugin.py (get_blueprint, get_models -> []).
- Fixed a latent bug in the move: error path used ErrorCodes.SERVER_ERROR which
  does not exist -> ErrorCodes.INTERNAL_ERROR.
- De-cored: deleted shopdb/core/api/slides.py, removed from CORE_BLUEPRINT_NAMES
  + core/api/__init__ import/__all__. Registered in instance/plugins.json.

Pinned with a characterization test first; passes unchanged against the plugin
blueprint. 174 tests pass, naming green, app boots 8 bundled plugins, /api/slides
verified live.

Note: the shopfloor dashboard is NOT extractable - it is a frontend-only Vue view
aggregating the businessunits + notifications APIs, with no backend to move and no
frontend plugin system.

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

plugins/slides/__init__.py

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+"""Slides plugin package."""
+
+from .plugin import SlidesPlugin
+
+__all__ = ['SlidesPlugin']

plugins/slides/api/__init__.py

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+"""Slides plugin API."""
+
+from .routes import slides_bp
+
+__all__ = ['slides_bp']

plugins/slides/api/routes.py

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+"""Slides API for the TV dashboard slideshow."""
+
+import os
+from flask import Blueprint, current_app
+
+from shopdb.api import success_response, error_response, ErrorCodes
+
+slides_bp = Blueprint('slides', __name__)
+
+# Valid image extensions
+VALID_EXTENSIONS = {'.jpg', '.jpeg', '.png', '.gif', '.bmp', '.webp'}
+
+
+@slides_bp.route('', methods=['GET'])
+def get_slides():
+    """Get list of slides for the TV dashboard.
+
+    Returns image files from the static/slides directory.
+    """
+    # Look for slides in static folder
+    static_folder = current_app.static_folder
+    if not static_folder:
+        static_folder = os.path.join(current_app.root_path, 'static')
+
+    slides_folder = os.path.join(static_folder, 'slides')
+
+    # Also check frontend public folder
+    frontend_slides = os.path.join(
+        os.path.dirname(os.path.dirname(os.path.dirname(current_app.root_path))),
+        'frontend', 'public', 'slides'
+    )
+
+    # Try multiple possible locations
+    possible_paths = [
+        slides_folder,
+        frontend_slides,
+        '/home/camp/projects/shopdb-flask/shopdb/static/slides',
+        '/home/camp/projects/shopdb-flask/frontend/public/slides',
+    ]
+
+    slides_path = None
+    for path in possible_paths:
+        if os.path.isdir(path):
+            slides_path = path
+            break
+
+    if not slides_path:
+        return success_response({
+            'slides': [],
+            'basepath': '/static/slides/',
+            'message': 'Slides folder not found'
+        })
+
+    # Get list of image files
+    slides = []
+    try:
+        for filename in sorted(os.listdir(slides_path)):
+            ext = os.path.splitext(filename)[1].lower()
+            if ext in VALID_EXTENSIONS:
+                slides.append({'filename': filename})
+    except Exception as e:
+        return error_response(
+            ErrorCodes.INTERNAL_ERROR,
+            f'Error reading slides: {str(e)}',
+            http_code=500
+        )
+
+    return success_response({
+        'slides': slides,
+        'basepath': '/static/slides/'
+    })

plugins/slides/manifest.json

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+{
+  "name": "slides",
+  "version": "1.0.0",
+  "description": "TV dashboard slideshow images served from a static folder",
+  "author": "ShopDB Team",
+  "dependencies": [],
+  "core_version": ">=0.1.0,<1.0.0",
+  "api_prefix": "/api/slides",
+  "provides": {
+    "features": ["slideshow"]
+  }
+}

plugins/slides/plugin.py

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+"""Slides plugin main class.
+
+Display/service plugin: contributes a blueprint only (no model, no AssetType,
+no nav). Serves TV-dashboard slideshow images. Demonstrates the minimal plugin
+shape - a feature that is purely an API surface.
+"""
+
+import json
+import logging
+from pathlib import Path
+from typing import List, Dict, Optional, Type
+
+from flask import Flask, Blueprint
+
+from shopdb.plugins.base import BasePlugin, PluginMeta
+
+from .api import slides_bp
+
+logger = logging.getLogger(__name__)
+
+
+class SlidesPlugin(BasePlugin):
+    """Slides plugin - TV dashboard slideshow images."""
+
+    def __init__(self):
+        self._manifest = self._load_manifest()
+
+    def _load_manifest(self) -> Dict:
+        """Load plugin manifest from JSON file."""
+        manifest_path = Path(__file__).parent / 'manifest.json'
+        if manifest_path.exists():
+            with open(manifest_path, 'r') as f:
+                return json.load(f)
+        return {}
+
+    @property
+    def meta(self) -> PluginMeta:
+        """Return plugin metadata."""
+        return PluginMeta(
+            name=self._manifest.get('name', 'slides'),
+            version=self._manifest.get('version', '1.0.0'),
+            description=self._manifest.get(
+                'description',
+                'TV dashboard slideshow images'
+            ),
+            author=self._manifest.get('author', 'ShopDB Team'),
+            dependencies=self._manifest.get('dependencies', []),
+            core_version=self._manifest.get('core_version', '>=0.1.0,<1.0.0'),
+            api_prefix=self._manifest.get('api_prefix', '/api/slides'),
+        )
+
+    def get_blueprint(self) -> Optional[Blueprint]:
+        """Return Flask Blueprint with API routes."""
+        return slides_bp
+
+    def get_models(self) -> List[Type]:
+        """No models - slides are read from the filesystem."""
+        return []
+
+    def init_app(self, app: Flask, db_instance) -> None:
+        """Initialize plugin with Flask app."""
+        logger.info(f"Slides plugin initialized (v{self.meta.version})")