fix: include actual error message in replaceable event rejection responses

[Priyanshubhartistm]

Description

ReplaceableEventStrategy.execute() sent clients a hardcoded error: command result (trailing space, no message) whenever eventRepository.upsert() rejected for any reason other than a duplicate event id constraint violation. The caught error.message was never included in the response. The command result now includes error.message, e.g. error: connection refused.

Related Issue

#710

Motivation and Context

Clients receiving ["OK", "<id>", false, "error: "] have no actionable information about why their event was rejected, which makes debugging relay-side failures (DB outages, connection issues, etc.) unnecessarily difficult for client authors and relay operators.

How Has This Been Tested?

• pnpm run test:unit — 1483 passing.
• pnpm run test:cli — 73 passing.
• pnpm run cover:unit — passing.
• pnpm run docker:test:integration — 99 scenarios / 489 steps passing.
• pnpm run lint, pnpm run check:deps, pnpm run build:check, pnpm run build,
  pnpm run verify:cli:build all pass.

Screenshots (if appropriate):

N/A — backend WebSocket message content change only.

Types of changes

• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• I added a changeset, or this is docs-only and I added an empty changeset.
• All new and existing tests passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 1cf5ded

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
nostream	Patch

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[coveralls]

coverage: 68.708%. remained the same — Priyanshubhartistm:fix/replaceable-event-error-message-empty into cameri:main