Use position "hidden" flag as source for identifying hidden position records

[kenkunz]

Goal

As a strategy admin, I want the source of data for identifying position records to be hidden in the UI to be the position record from the trade-executor state API payload.

Background

• see Hide flagged strategy positions #812
• see Add "hidden" flag to TradingPosition records that should be hidden in the UI trade-executor#1041

Acceptance criteria

Given: a position that has been flagged as hidden on the backend (see tradingstrategy-ai/trade-executor#1041):

1. For non-admin users
   1. the position is hidden on the strategy positions table
   2. the route for the position details returns a 404 Not found
2. For admin users
   1. the position is included on the strategy positions table with a hidden badge shown and reduced opacity on the table row to indicate that this position would be hidden for non-admin users
   2. the route for the position details displays the position, with a hidden badge
3. The frontend strategy config no longer includes hiddenPositions array (this was a stop-gap solution until we had the proper backend solution)