Remove ASTER, PUMP, ZEC from dashboard and stop tracking their history

- Remove ASTER, PUMP, ZEC from WATCHED_COINS in main_app.py
- Remove ASTER, PUMP, ZEC from coin_id_map.json (stops market cap collection)
- Remove ASTER, PUMP, ZEC from market_cap_data.json summary
- Remove ASTER, PUMP, ZEC manual overrides from coin_id_map.py
- Remove ASTER, PUMP, ZEC from resampling_status.json (gitignored)
- Add WIKI/symbol_management.md documentation for adding/removing symbols

Existing data in market_data.db is preserved; only new data collection stops.

coin_id_map.py

@@ -52,9 +52,6 @@ def update_coin_mapping():
         "SOL": "solana",
         "BNB": "binancecoin",
         "HYPE": "hyperliquid",
-        "PUMP": "pump-fun",
-        "ASTER": "astar",
-        "ZEC": "zcash",
         "SUI": "sui",
         "ACE": "endurance",
         # Add other important ones you watch here