Add toast notification on successful key buy or sell transaction

[Chucks1093]

Summary

After a buy or sell transaction confirms on-chain, the user receives no visual feedback beyond the modal closing. A toast notification confirming the action, the quantity, and the creator name should appear briefly after the transaction settles.

Scope

• Show a success toast after a confirmed buy: Bought {n} key{s} from {creator}
• Show a success toast after a confirmed sell: Sold {n} key{s} from {creator}
• Toast should auto-dismiss after 4 seconds
• Error toasts for failed transactions are a separate issue — do not include here

Acceptance Criteria

• Success toast appears after buy confirmation
• Success toast appears after sell confirmation
• Toast content includes quantity and creator name
• Toast auto-dismisses after 4 seconds

ETA: 12 hours

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Coordinate on Telegram

[GBOYEE]

Hi maintainers, I can handle this one. I'll implement it to spec and add tests. I'll open a PR referencing this shortly once assigned.

[Tijesunimi004]

I havee experience with Open SOurce and would like to work on this issue

[grantfox-oss]

🦊 GrantFox — @Tijesunimi004 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #540)
2. Your PR will be reviewed by the accesslayerorg maintainers

Good luck! Track your progress on GrantFox.