docs: add Base Account provider capabilities troubleshooting

[tung39838]

What changed? Why?

Many integration issues are not caused by incorrect Base Account usage, but by:

• Wallets that do not implement the required methods.

• Missing capability detection before execution.

• Incorrect provider initialization.

• Unsupported RPC method assumptions.

A dedicated troubleshooting page reduces repetitive support questions and improves developer onboarding.

This aligns with the project's emphasis on helping developers reach the "happy path" quickly while still documenting alternative paths.

Notes to reviewers

• No new top-level documentation sections are introduced.

• The page follows the existing troubleshooting pattern.

• Examples use capability detection rather than wallet-specific behavior.

• The content is intentionally focused on the most common provider capability failures to avoid overlap with the Reference section.

[cb-heimdall]

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