feat: support custom doc scripts

[DevDengChao]

Summary

• Add backend customJavaScriptUrls setting support for Knife4j doc.html extension scripts.
• Load configured scripts in Vue2/Vue3 doc initialization and expose window.Knife4j.registerRequestInterceptor for debug request customization.
• Apply request interceptors to url-form, form, and raw debug requests so injected headers are sent and reflected in curl output.
• Document usage, security notes, and the difference from AfterScript.
• Add Spring configuration binding tests for OpenAPI2 and OpenAPI3 Jakarta starters.

Test Plan

• node tests/custom-script-extension.test.cjs
• mvn -pl knife4j-openapi2-spring-boot-starter,knife4j-openapi3-jakarta-spring-boot-starter -am -Dknife4j-skipTests=false "-Dspotless.apply.skip=true" test
• mvn -pl knife4j-core,knife4j-openapi2-spring-boot-starter,knife4j-openapi3-spring-boot-starter,knife4j-openapi3-jakarta-spring-boot-starter -am -DskipTests "-Dspotless.apply.skip=true" compile

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