Finish axios migration via shared native HTTP helper

Replace all in-scope axios callsites with a new helpers/http.js wrapper over native fetch, including JSON/text GET, JSON POST, HEAD checks, and transient 5xx retry behavior; update all browser, build, script, and proxy API clients to use it; add focused unit tests; and remove axios from package dependencies.

Constraint: Preserve API/build and deployment behavior while lowering transport surface area.

Rejected: inline fetch replacements at each callsite | rejected to avoid inconsistent error/retry semantics.

Confidence: high

Scope-risk: moderate

Directive: Keep helper in place as the transport boundary and update tests when changing request semantics.

Tested: pnpm run -s typecheck, pnpm -s run test-prebuild, pnpm -s run test, pnpm -s run test:browser, pnpm -s run netlify-build, smoke GETs on /apple-silicon-app-test and /apple-silicon-app-test/?version=2

Not-tested: branch/netlify deployment health in CI pipeline after merge

helpers/api/sitemap/parse.js

@@ -1,6 +1,5 @@
 import path from 'path'
 import fs from 'fs-extra'
-import axios from 'axios'
 import { parse } from 'fast-xml-parser'
 
 import {
@@ -8,6 +7,10 @@ import {
     sitemapIndexFileName,
 } from '~/helpers/constants.js'
 import { isValidHttpUrl } from '~/helpers/check-types.js'
+import {
+    getText,
+    headOk
+} from '~/helpers/http.js'
 
 const sitemapFilesToTry = [
     sitemapIndexFileName,
@@ -106,12 +109,7 @@ export async function fetchAllUrlsFromSitemaps ( urlString ) {
         // console.log( 'sitemapUrl', sitemapUrl.href )
 
         // Just do a quich HEAD request to see if the file exists with getting the whole body
-        const exists = await axios.head( sitemapUrl.href )
-            .catch( () => false )
-            .then( response => {
-                // console.log( 'response', response.status )
-                return response.status < 300
-            } )
+        const exists = await headOk( sitemapUrl.href )
 
         // console.log( 'exists', exists )
 
@@ -123,8 +121,7 @@ export async function fetchAllUrlsFromSitemaps ( urlString ) {
             getMethod: async sitemapPath => {
                 const sitemapUrl = new URL( sitemapPath, urlString )
 
-                const sitemapXml = await axios.get( sitemapUrl.href )
-                    .then( response => response.data )
+                const sitemapXml = await getText( sitemapUrl.href )
 
                 return sitemapXml
             }