chore: fix Vertex AI global region URL in LlmClient (backport)

[davsclaus]

Straight cherry-pick backport of #25936 (squash-merged as e3f7f4c on main) onto camel-4.22.x. No conflicts.

Summary

• LlmClient.resolveAnthropicUrl() built the Vertex AI Anthropic endpoint by always prefixing the host with <region>-. That's correct for regional locations (e.g. us-east5) but wrong for the global location, whose actual host is aiplatform.googleapis.com with no region prefix.
• With CLOUD_ML_REGION=global set, requests went to the non-existent host global-aiplatform.googleapis.com, causing the TUI's F8 AI panel and camel ask/explain/harden to fail with a generic "LLM request failed" error whenever the Vertex AI auto-detect path was used with the global region.

Test plan

• mvn -q -DskipTests install on camel-jbang-core (this branch)
• Clean cherry-pick, no conflicts

Claude Code on behalf of davsclaus

🤖 Generated with Claude Code

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🧪 CI tested the following changed modules:

• dsl/camel-jbang/camel-jbang-core

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🔬 Scalpel shadow comparison — Scalpel: 7 tested, 8 compile-only — current: 6 all tested

Maveniverse Scalpel detected 15 affected modules (current approach: 6).

⚠️ Modules only in Scalpel (9)

• camel-jbang-core
• camel-jbang-it
• camel-jbang-main
• camel-jbang-plugin-edit
• camel-jbang-plugin-generate
• camel-jbang-plugin-kubernetes
• camel-jbang-plugin-test
• camel-launcher
• coverage

Skip-tests mode would test 7 modules (1 direct + 6 downstream), skip tests for 8 (generated code, meta-modules)

Modules Scalpel would test (7)

• camel-jbang-core
• camel-jbang-mcp
• camel-jbang-plugin-mcp
• camel-jbang-plugin-route-parser
• camel-jbang-plugin-tui
• camel-jbang-plugin-validate
• camel-launcher-container

Modules with tests skipped (8)

• camel-jbang-it
• camel-jbang-main
• camel-jbang-plugin-edit
• camel-jbang-plugin-generate
• camel-jbang-plugin-kubernetes
• camel-jbang-plugin-test
• camel-launcher
• coverage

ℹ️ Shadow mode — Scalpel observes but does not affect test execution. Learn more

⚠️ Some tests are disabled on GitHub Actions (@DisabledIfSystemProperty(named = "ci.env.name")) and require manual verification:

• dsl/camel-jbang/camel-jbang-core: 1 test(s) disabled on GitHub Actions

💡 Manual integration tests recommended:

You modified dsl/camel-jbang/camel-jbang-core. The related integration tests in dsl/camel-jbang/camel-jbang-it are excluded from CI. Consider running them manually:

mvn verify -f dsl/camel-jbang/camel-jbang-it -Djbang-it-test

All tested modules (15 modules)

• Camel :: Coverage
• Camel :: JBang :: Core
• Camel :: JBang :: Integration tests
• Camel :: JBang :: MCP
• Camel :: JBang :: Main
• Camel :: JBang :: Plugin :: Edit
• Camel :: JBang :: Plugin :: Generate
• Camel :: JBang :: Plugin :: Kubernetes
• Camel :: JBang :: Plugin :: MCP
• Camel :: JBang :: Plugin :: Route Parser
• Camel :: JBang :: Plugin :: TUI
• Camel :: JBang :: Plugin :: Testing
• Camel :: JBang :: Plugin :: Validate
• Camel :: Launcher
• Camel :: Launcher :: Container

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