feat: support claude custom url

[ThxCode-Chen]

Ⅰ. Describe what this PR did

Synchronizes the claudeCustomUrl configuration support for the Claude (Anthropic) provider in plugins/wasm-go/extensions/ai-proxy with the implementation used in the main Higress tree.

provider/provider.go: Adds the claudeCustomUrl field on ProviderConfig (with metadata comments) and parses it from JSON in FromJson.

provider/claude.go: When claudeCustomUrl is set, parses host and path (supports plain origin, path prefix, or a direct /v1/messages URL), adjusts capabilities accordingly, stores custom domain for outbound requests, and keeps the default behavior when the field is empty. TransformRequestHeaders uses the custom host when configured; otherwise it still uses resolveDomain("", claudeDomain) so providerDomain and other domain overrides keep working.

test/claude.go: Adds WASM integration-style tests for config load and for :authority being rewritten to the custom host.

Ⅱ. Does this pull request fix one issue?

No. This is a parity / sync change; there is no linked issue.

Ⅲ. Why don't you add test cases (unit test/integration test)?

Integration coverage was added in test/claude.go (plugin config + request headers). No extra unit tests were added in provider/claude_test.go because the main Higress reference implementation does not add separate CreateProvider / claudeCustomUrl unit tests there either; behavior is covered at the integration layer.

Ⅳ. Describe how to verify it

From plugins/wasm-go/extensions/ai-proxy:
go test ./provider/... ./test/... -count=1
Manually: configure a Claude provider with claudeCustomUrl (e.g. https://custom.example.com/anthropic) and confirm upstream requests use the expected Host and path for chat/messages traffic.

Ⅴ. Special notes for reviews

Interaction with providerDomain: Custom URL host wins when claudeCustomUrl is set; when it is unset, existing resolveDomain behavior is unchanged.

Capabilities: Logic matches the main repo: a direct messages endpoint only overrides message-related paths; otherwise the configured path acts as a prefix for default capability paths.

Ⅵ. AI Coding Tool Usage Checklist (if applicable)

Please check all applicable items:

• [√ ] For new standalone features (e.g., new wasm plugin or golang-filter plugin):

  • I have created a design/ directory in the plugin folder
  • I have added the design document to the design/ directory
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• For regular updates/changes (not new plugins):

  • I have provided the prompts/instructions I gave to the AI Coding tool below
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AI Coding Summary

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.33333% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ins/wasm-go/extensions/ai-proxy/provider/claude.go	84.61%	2 Missing and 2 partials ⚠️

📢 Thoughts on this report? Let us know!

[CH3CHO]

Please sign the CLA. Thanks. @ThxCode-Chen

[ThxCode-Chen]

/review

[ThxCode-Chen]

Please sign the CLA. Thanks. @ThxCode-Chen

I have signed the CLA, but it looks not completed yet. Can you help me check where is wrong?@CH3CHO

[CH3CHO]

Please sign the CLA. Thanks. @ThxCode-Chen

I have signed the CLA, but it looks not completed yet. Can you help me check where is wrong?@CH3CHO

I've re-triggered the CLA check. It looks good now. Thanks.

[CH3CHO]

LGTM

[ThxCode-Chen]

Please help review the code. Thanks.@johnlanni @rinfx @wydream

[CH3CHO]

Please resolve conflicts. @ThxCode-Chen

[wydream]

@ThxCode-Chen #3686 has already implemented the claudeCustomUrl capability via providerDomain and providerBasePath.