Document which of the seven listed chains actually have working integrations

[james2177]

Description

SupportedChain in src/intents/intents.types.ts lists seven chains (stellar, ethereum, base, polygon, arbitrum, optimism, avalanche), but only Stellar has any real integration (SorobanService) — the README doesn't currently clarify this gap, which could mislead a contributor or integrator into thinking all seven are equally supported.

Requirements and context

• Add a clear "supported vs. planned" matrix to the README, consistent with how the roadmap section already flags what's live vs. pending

Suggested execution

1. Fork the repo and create a branch

   git checkout -b docs/supported-chains-matrix
   

2. Implement changes
   Relevant files:

• README.md

3. Test and commit

   • Run npm run lint && npm run typecheck && npm test && npm run test:e2e
   • Include test output / screenshots or logs demonstrating the fix in the PR

   Example commit message:

   docs: document which supported chains have working integrations
   

Guidelines

• Assignment required before starting — comment to claim this issue
• PR description must include: Closes #[this issue's number]
• Timeframe: 96 hours from assignment
• Complexity: High (200 points)

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Part of the Drips Wave for vortex-backend.