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

scripts/vercel-post-deploy/index.js

@@ -1,6 +1,6 @@
 import { isMacOS } from 'std-env'
 
-import axios from 'axios'
+import { getText } from '~/helpers/http.js'
 
 ;(async () => {
 
@@ -10,7 +10,7 @@ import axios from 'axios'
         process.exit()
     }
 
-    const { data } = await axios.get(`https://master--doesitarm.netlify.app/apple-silicon-app-test`)
+    const data = await getText( 'https://master--doesitarm.netlify.app/apple-silicon-app-test' )
 
     console.log( data.slice(0, 100) )