fix: add Base to default chains so its icon renders out of the box

[tenderdeve]

Summary

• Base (chain ID 8453) had its icon SVG added in add: zora + base logos #418 but was not included in the default chains array
• The chain icon mapping was never triggered because Base wasn't in the list
• Add base to the default chains in defaultConfig.ts and defaultTransports.ts

Files:

• packages/connectkit/src/defaultConfig.ts
• packages/connectkit/src/defaultTransports.ts

Fixes #438

Test plan

• Base chain icon renders in the network selector without custom config
• Other chain icons (Arbitrum, Mainnet, Polygon, Optimism) still render
• Default config connects to Base correctly

[vercel]

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