[karagozemin]

Closes #515

Summary

• open Horizon transaction SSE with explicit event-count and duration bounds
• incrementally decode and display event type and JSON payload
• abort on bound, manual stop, replacement run, or component unmount
• report connected/disconnected and empty-sample outcomes explicitly
• add the complete 35-file feature slice and focused coverage

Verification

• npm run verify:features -- horizon-stream-sampler
• npx eslint features/horizon-stream-sampler (0 errors)
• npx vitest run features/horizon-stream-sampler (16 tests passed)
• npx tsc --noEmit

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