fix(search): relay API error messages for every search, not only Alexandria ones

[nickscamara]

firecrawl_search only routed errors through relayExchangeError when sources included alexandria. When an agent passed its own non-Alexandria sources (["web"], ["news"], ...), the call went through relayTermsRequired, which rethrows the raw axios error from client.http.post. The agent then saw Request failed with status code 402 with the API's out-of-credits message and upgrade link stripped. Default searches and scrapes were unaffected because they already used relayExchangeError or the SDK's own error normalization.

• Both search entry points (src/server.ts and the hosted src/service/search-surface.ts) now always use relayExchangeError, which still handles the terms-required case and still leaves 401s to credential recovery.
• The fallback message for an error body without an error string now says Firecrawl request failed (HTTP N) instead of Alexandria request failed, since it is no longer Alexandria-only.
• New test: a 402 with the API's credits message is relayed verbatim for default, ["web"], ["news"] and ["alexandria"] searches. It failed before the fix with the bare axios message.

No version bump or changelog entry; leaving that to the release.

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Summary by cubic

Fixes firecrawl_search error handling so non-Alexandria searches (e.g. ["web"], ["news"]) surface the API's actual error message. Previously these went through relayTermsRequired, which rethrew the raw axios error — a 402 showed only "Request failed with status code 402" and dropped the out-of-credits message and upgrade link. Version 3.30.2 is bumped with a changelog entry for the fix.

• Both search entry points (src/server.ts and src/service/search-surface.ts) now always use relayExchangeError, which still handles the terms-required case.
• The fallback message for an error body without an error string now reads Firecrawl request failed (HTTP N) instead of Alexandria request failed.
• New test verifies a 402 with the API's credits message is relayed verbatim for default, ["web"], ["news"], and ["alexandria"] searches.

^{Written for commit a38fcf4. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

<sub>Auto-approved: Fixes firecrawl_search to always use relayExchangeError so API error messages surface for non-Alexandria sources; a focused error-handling fix with a new test covering default, web, news, and alexandria searches.

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