fix: add missing ft_metadata view function to fungible token example - #428

Summary

• The my-ft example defines and stores FungibleTokenMetadata but never exposes it via a view function, violating NEP-148
• Add ft_metadata() view function and implement FungibleTokenMetadataProvider interface
• Follows the same pattern used by the NFT example (my-nft.ts line 173)

File: examples/src/fungible-token/my-ft.ts

Fixes #415

Test plan

• Build the example: pnpm build
• Call ft_metadata on a deployed instance — should return the metadata object
• Existing FT tests pass