feat: integrate PolkaGate extension wallet

[AMIRKHANEF]

Pull Request Summary

This PR adds full PolkaGate extension integration to the Astar dApp, allowing users to connect their Astar accounts directly through PolkaGate.

Check list

• contains breaking changes
• adds new feature
• modifies existing feature (bug fix or improvements)
• relies on other tasks
• documentation changes
• tested on mobile devices

This pull request makes the following changes:

Adds

• Add PolkaGate to SupportWallet enum
• Add PolkaGate to SubstrateWallets array
• Add PolkaGate configuration block inside supportWalletObj (name, logo, links, extension flags)
• Add logo_polkagate.png to src/assets/img/

Fixes

• N/A (no fixes included)

Changes

• Extends the wallet configuration to support an additional Substrate wallet provider
• No existing behavior modified

To-dos

None