Add ISIN codes for ETFs

[AlfaStake]

Summary

• Added isin column to database/etfs.csv with 6,001 ISIN codes matched across {total} ETFs.

ISIN column added — methodology

• I did not match by symbol, because tickers differ across data sources and exchanges.
• I matched using a normalized name: removed share-class suffixes, punctuation, and extra spaces.
• 100% matches only (token_sort_ratio) — no approximate fuzzy matching.
• Reference sources with priority: JustETF → Morningstar → ESMA Securities Database.
• 6,001 ISIN matched out of 36,554 ETFs in the database.

This approach is more robust than symbol-based matching because tickers change across exchanges
(e.g., IWDA.AS vs IWDA.L vs EUNL.DE refer to the same ETF). The normalized name is a more stable identifier.