feat(monitoring): add priority screenshot pipeline with screenshot_type + docs cleanup

Implement end-to-end support for typed screenshots and priority rendering in monitoring.

Added
- Accept and forward screenshot_type from MQTT screenshot/dashboard payloads
  (periodic, event_start, event_stop)
- Extend screenshot upload handling to persist typed screenshots and metadata
- Add dedicated priority screenshot serving endpoint with fallback behavior
- Extend monitoring overview with priority screenshot fields and summary count
- Add configurable PRIORITY_SCREENSHOT_TTL_SECONDS window for active priority state

Fixed
- Ensure screenshot cache-busting updates reliably via screenshot hash updates
- Preserve normal periodic screenshot flow while introducing event_start/event_stop priority path

Improved
- Monitoring dashboard now displays screenshot type badges
- Adaptive polling: faster refresh while priority screenshots are active
- Priority screenshot presentation is surfaced immediately to operators

Docs
- Update README and copilot-instructions to match new screenshot_type behavior,
  priority endpoint, TTL config, monitoring fields, and retention model
- Remove redundant/duplicate documentation blocks and improve troubleshooting section clarity

server/wsgi.py

@@ -68,6 +68,16 @@ def index():
     return "Hello from Infoscreen‐API!"
 
 
+@app.route("/screenshots/<uuid>/priority")
+def get_priority_screenshot(uuid):
+    normalized_uuid = uuid[:-4] if uuid.lower().endswith('.jpg') else uuid
+    priority_filename = f"{normalized_uuid}_priority.jpg"
+    priority_path = os.path.join("screenshots", priority_filename)
+    if os.path.exists(priority_path):
+        return send_from_directory("screenshots", priority_filename)
+    return get_screenshot(uuid)
+
+
 @app.route("/screenshots/<uuid>")
 @app.route("/screenshots/<uuid>.jpg")
 def get_screenshot(uuid):