feat: add GET /tokens endpoint listing tokens across streams

[PHADAR6]

Overview

This PR adds a GET /tokens endpoint that returns the distinct tokenAddress values seen across streams, along with a stream count for each. This lets the frontend populate a token filter from real data instead of relying on hardcoded values.

Related Issue

Changes

🪙 Tokens Aggregation Endpoint

• [MODIFY] src/routes/streams.ts

  • Adds a GET /tokens handler that aggregates streams by tokenAddress and returns each distinct token with its stream count.

• [MODIFY] src/server.ts

  • Registers the streams router so the new /tokens route is reachable.

• [MODIFY] test/routes/streams.test.ts

  • Adds a test asserting the aggregation returns distinct tokenAddress values with correct stream counts.

Verification Results

npm run lint
npm run typecheck
npm test

Acceptance Criteria	Status
Add GET /tokens returning distinct tokenAddress values with a stream count for each	✅ Implemented in src/routes/streams.ts
Add a test asserting the aggregation	✅ Added to test/routes/streams.test.ts

Closes #107

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