build(frontend)!: knip drops --production; plain knip stays

The production pass (7ed2ac4e, E32) asked "is this export used by what
ships?". No real hit: its only findings were 37 exports a test imports,
answered with 36 `@internal` JSDoc tags (E34 S2) — test-only exports, not
defects. Since then it has only ever asked for another tag. The tags go
with it (36, no longer read by anything), and so do the production-only
`!…!` exclusions in knip.jsonc and their register rows. Plain knip (unused
files, exports and dependencies) keeps running in the gate.

frontend/src/lib/issueDraft.ts

@@ -58,7 +58,6 @@ export function draftSteps(
 
 /** The operating system a user agent names. Checked most specific first: Android's agent also says
  *  "Linux" — and says it first — and an iPad's also says "Mac OS X". */
-/** @internal exported for issueDraft.test.ts */
 export function osName(ua: string): string {
   const tests: [RegExp, (m: RegExpExecArray) => string][] = [
     [/Android [\d.]+/, (m) => m[0]],