perf: Polling worker fetches all pending events in one unbounded request — add pagination

[Xhristin3]

Problem Statement
worker.ts calls GET /streams/pending and expects an array of all pending events. With no pagination, a backlog of thousands of events is returned in a single HTTP response, consuming significant memory.

Why It Matters
An unbounded poll response is a memory bomb during catch-up after downtime. It also makes the worker's memory footprint unpredictable.

Acceptance Criteria

• GET /streams/pending supports limit and cursor/offset query parameters
• Worker fetches events in batches (configurable via POLL_BATCH_SIZE env var, default 100)
• Worker continues fetching until the batch is smaller than POLL_BATCH_SIZE
• POLL_BATCH_SIZE documented in xstreamroll-processing/.env.example

Files Affected: xstreamroll-processing/src/worker.ts, api/src/streams/streams.controller.ts

Difficulty: Medium | Effort: 1–2 days

[irefavor15-dotcom]

Hello Maintainer
can you kindly assign me this issue to work on

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #337)
2. Your PR will be reviewed by the XStreamRollz maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@irefavor15-dotcom's PR #475 was approved and merged by @Xhristin3.

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