feat(ai-proxy): add UnauthorizedError/TooManyRequestsError and typed AI provider errors

[Scra3]

Summary

• Add UnauthorizedError (401) and TooManyRequestsError (429) to agent-toolkit, re-exported from datasource-toolkit
• Add httpCode property to BusinessError and all subclasses
• Add corresponding cases in the agent's error-handling middleware
• Create typed AI provider errors in ai-proxy:
  • AIProviderError — generic provider error (builds message from cause)
  • AITooManyRequestsError — wraps 429 from providers
  • AIUnauthorizedError — wraps 401 from providers
• Refactor wrapProviderError to use typed errors instead of generic AIUnprocessableError
• Add hierarchy tests for new error classes

[qltysh]

3 new issues

Tool	Category	Rule	Count
qlty	Structure	Function with many returns (count = 8): getErrorStatus	2
qlty	Structure	Function with many parameters (count = 4): constructor	1

[qltysh]

Coverage Impact

⬆️ Merging this pull request will increase total coverage on main by 0.01%.

Modified Files with Diff Coverage (6)

Rating	File	% Diff	Uncovered Line #s
	packages/ai-proxy/src/provider-dispatcher.ts	100.0%
	packages/ai-proxy/src/errors.ts	100.0%
	packages/datasource-toolkit/src/errors.ts	100.0%
	packages/agent/src/routes/system/error-handling.ts	100.0%
	packages/agent-toolkit/src/errors.ts	100.0%
	packages/agent/src/types.ts	100.0%
	Total	100.0%

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• Diff Coverage: Coverage for added or modified lines of code (excludes deleted files). Learn more.

• Total Coverage: Coverage for the whole repository, calculated as the sum of all File Coverage. Learn more.

• File Coverage: Covered Lines divided by Covered Lines plus Missed Lines. (Excludes non-executable lines including blank lines and comments.)

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