Add first-class Swig MCP wallet support

[edo-chan]

Summary

• add a first-class swig Solana signing mode to setup/config and surface the Swig wallet metadata SolClaw needs
• pass Swig secrets through the container boundary, register the Swig MCP server in the agent runner, and expose mcp__swig_wallet__* tools when Swig is configured
• route the agent skills toward Swig MCP usage, add env/config tests, and document the new support path

Validation

• npm run typecheck
• npm run build
• npm test -- src/env.test.ts src/solana/config.test.ts src/container-runner.test.ts setup/environment.test.ts
• npm run build (in container/agent-runner)
• npx tsx setup/index.ts --step solana --network devnet --signing-method swig --swig-fee-mode self-funded

Notes

• direct push to the upstream repo was not permitted from this machine, so this PR comes from the edo-chan/solclaw fork